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3 



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L 




ELEMENTS 



GEOLOGY. 




CHARLES LYELL, ESQ. F.R.S. 



AUTHOR OF ' 



OP GBOLOGT." 



"It |j«phi!D«ophT which nererniti— ill law taprogreu! ■ ftiot 
hich rettfirday vob iuvltlbLe It tu gorJ to^di^, and will bs Iti ituUiiff 
jWto-mot.ow."— Edw. R(v., No.isa. p.83. July 1837. 



LONDON; 
JOHN MURRAY, ALBEMARLE STREET. 



170. 



f 
t 



London : 

PriBted by A, Spottiswoops, 

New-Street- Square. 



TO 

WILLIAM HENRY FITTON, 

M.D. F.R.S. 

VICE-PRESIDENT OF THE GEOLOGICAL SOCIBTT, 

ETC. 



My bear Dr. Fitton, 

I HAVE great pleasure in dedicating 
this volume to you, as a memorial of an 
uninterrupted friendship of nearly twenty 
years, daring which we have been engaged 
in the same scientific pursuits. I am also 
glad to have this opportunity of acknow- 
ledging the benefit which my writings 
have so often derived from your friendly 

criticism. 

I am. 

My dear Dr. Fitton, 

Yours, very sincerely, 

CHARLES LYELL. 



LovDOM, July 26. 1838. - 

A 2 



PREFACE. 



Part of the present Treatise was written origin- 
ally in the form of a supplement to my former 
work, entitled " Principles of Geology," and was 
intended for the use of those students who found 
certain chapters in the Principles obscure and 
difficult, for want of preliminary information. I 
afterwards considered that it would not be incom- 
patible with this object to enlarge the Elements 
into a separate and independent treatise, to serve 
as an introduction to Geology proper. As I have 
thus been led on to become the author of two 
general works on the same science, it may be useful 
to explain to the reader that these two publications 
do, in fact, occupy very distinct ground. 

In the Principles a systematic account is given 
of the operations of inorganic causes, ' such as 
rivers, springs, tides, currents, volcanos, and earth- 
quakes ; the effects of all being particularly con- 
sidered, with a view to illustrate geological phe- 
nomena. The changes also which the organic 
world has undergone in modern times, the geo- 
graphical distribution of different species of ani- 

a3 



^1 PREFACE. 

mals and plantp, the causes of tbeir wultiplicatiop 
and 'Extinction, and their first intrpductioi^,. ari^ 
discussed, and the yarious ways in \«4xici^ dU^ir 
l*ecnains become fossil in aetr deposits* The: pt^u- 
dent) who is familiar with thia the larger portion 
of the Principles (comprising no less than jSy^ 
sixths of the whole), will, it is hoped» more easily 
Comprehend the expluiations of geoU^^ioal appear*- 
toieeB proposed in the Elements. On Ae otb^ 
hand, those who begin with the Elements, the 
scope of iwhich may be understood by a glance a^t 
the annexed table of contents, will follow u^me 
easi}y the meaning of that pmrt of th^ Princi|^^ 
in which an attempt is made to point out tlie 
bearing on geology of the modem changes of the 
earth, and to which is prefixed a history of die 
opinions which have been entertained in this 
s<Henee, from the times of the earliest writers to 
the present day. 

The volume, therefore, now offered to the pub- 
lic, is neither an epitome of the Principles, nor an 
abridgement of any part of that work. In some 
places, where I thought it desirable to incorporate 
in the Elements certain passages of the former 
work, I have not abridged what was previously 
written, but have expanded it, giving fuller ex- 
planations, and additional wood-cuts, in the hope 
of rendering it more intelligible to the beginner. 

Through the kindness of two of my friends I 



PREFACE. VU 

have been enabled to refer frequently to two 
works, not yet before the public^ Mr* Darwin'g 
Joomdl of Travels in South America, 1832 to 
1836, Sccy and Mr. Murchison's Silurian System; 
the last of which was presented to me complete, 
with the exception of the maps and plates, and 
will shortly be published. 

Mr. Darwin's Journal was finished, and ready 
for publication, some time before the printing of 
niy MS. had begun, but is still detained, to the 
great regret of the scientific world, because it is to 
form part of a larger work, including an account 
of the Surreys of Captains King and FitaRoy, in 
South America. 

N« B. The greater part of the woodcuts in this volume, 
especially those most difficult of execution, are the work of 
Mr. James Lee, 97, Princes Square, Kennington. The 
original drawings in Natural History were done by Mr. Geo. 
Sowerfoy, jun., 14, Tibberton Square, Lower Road, Islington. 



A 4 



CONTENTS. 



PART I. 

CHAPTER I. 

ON THE FOUR GREAT CLASSES OF ROCKS THE AQUEOUS, 

VOLCANIC, PLUTONIC, AND METAMORPHIC. 

Geology defined — Successive formation of the earth's crust 
— Classification of rocks according to their origin and 
age — Aqueous rocks (p. 5.) — Their stratification and 
imbedded fossils — Volcanic rocks, with and without cones 
and craters (p. 11.) — Plutonic rocks, and their relation 
to the volcanic — Metamorphic rocks, and their probable 
origin (p. 17.) — The term primitive, why erroneously ap- 
plied to the crystalline formations (p. 21.) — Division of 
the work into two parts ; the first descriptive of rocks 
without reference to their age, the second treating of their 
chronology. 

CHAPTER 11. 

AQUEOUS ROCKS THEIR COMPOSITION AND FORMS OF 

STRATIFICATION. 

Mineral composition of strata — Arenaceous rocks — Argil- 
laceous — Calcareous — Gypsum — Forms of stratification 
(p. 32.) — Original horizontality — thinning out — Diago- 
nal arrangement (p. 38.) — Ripple mark. 

A 5 



y CONTENTS. 

— CHAPTER III. 

ARRANGEMENT OF FOSSILS IN STRATA — FRESHWATER AND 

MARINE. 

Successive deposition indicated by fossils — Limestones 
formed of corals and shells — Proofs of gradual increase 
of strata derived from fossils — Serpula attached to spa- 
tangus (p. 48.) —"Wood bored by teredina — Tripoli and 
semi-opal formed of infusoria — Chalk derived principally 
from organic bodies (p. 55.) — Distinction of freshwater 
from marine formations ~- Genera of freshwater and land 
shells — Rules for recognizing marine testacea — Gyro- 
gonite and chara (p. 66.) — Freshwater fishes — Alterna- 
tion of marine and freshwater deposits — Lym-Fiord. 

CHAPTER IV. 

CONSOLIDATION OF STRATA AND PETRIFACTION OF 

FOSSILS. 

Chemical and mechanical deposits — Cementing together of 
partides -— Hardening by exposure to air (p. 74.)— Con- 
cretionary nodules — ConsolidMing effects of pressure — 
Mineralization of organic remains (p. 79.) — Impressions 
and casts how formed — Fossil wood^ — Goppert's experi- 
ments — Precipitation of stony matter most rapid where 
putrefaction is going on — Source of lime in solution 
(p. 87.) — Silex derived from decomposition of felspar-— 
Proofs of the lapidification of soo^e fossils soon after burial, 
of others when much decayed. 

CHAPTER V. 

ELEVATION OF STRATA ABOVE THE SEA — HORIZONTAL 
AND INCLINED STRATIFICATION. 

Why the elevated position of marine strata should be re- 
ferred to the rising up of the land, not to the going down 
of the sea — Upheaval of ^tensive masaea of •horizoatal 



CONTENTS. XI 

Strata (p. 95.) — Inclined and irertical stra^cation — 
Anticlinal and synclinal lines — Examples of bent strata 
in east of Scotland (p. 101.) — Theory of folding by lateral 
moyement — Dip and strike (p. J 05.)—- Structure of the 
Jura — Rocks broken by flexure — Inverted position of 
disturbed strata (p. 113.) — Unconformable stratification 
— Fractures of strata — Polished surfaces -^Faults — 
Appearance of repeated alternations produced by them 
(p. 119.) — Origin of great faults. 

CHAPTER VL 

DKNUDATIOy, AND THE PRODUCTION OF AtLUVIUM. 

Denudation defined — Its amount equal to the entire mass 
of stratified deposits in the earth's crust — Horizontal 
sandstone denuded in Ross-shire — Levelled surface of 
countries in which great faults occur (p. 127.) — Con- 
nexion of denudation and alluvial formations — Alluvium, 
how distinguished from rocks in situ (p. 132.) — Ancient 
alluviums called diluvium — Origin of these — Erratic 
blocks and accompanying gravel (p. 135.) — Theory of 
dieir transportation by ice. 

CHAPTER VII. 

VOLCANIC ROCKS. 

IVap roc^s — Name, whence derived — Their igneous origin 
at first doubted — Their general appearance and character 
— Volcanic cones and craters, how formed (p. 144.)-— 
Mineral composition and texture of volcanic rocks — 
Varieties of felspar — Hornblende and augite — Isomor- 
phism (p. 151.) — Rocks, how to be studied — Basalt, 
greenstone* trachyte, porphyiy, scoria, amygdaloid (p. 155.) 
lava, tuff— Alphabetical list, and explanation of names 
and synonyms, of volcanic rocks (p. 161.) — Tabic of the 
analyses of minerals most abundant in the volcanic and 
hypogene rocks. 



Xll CONTENTS, 



CHAPTER VIII. 
VOLCANIC ROCKS — continued. 

Trap dikes — sometimes project — sometimes leave fissures 
vacant by decomposition — Branches and veins of trap — 
Dikes more crystalline in the centre (p. 172.) — Foreign 
fragments of rock imbedded — Strata altered at or near 
the contact — Obliteration of organic remains — Conver- 
sion of chalk into marble — and of coal into coke (p. 178.} 
— Inequality in the modifying influence of dikes — Trap 
interposed between strata — Columnar and globular struc- 
ture (p. 182.) — Relation of trappean rocks to the pro- 
ducts of active volcanos (p. 188.) — Submarine lava and 
ejected matter corresponds generally to ancient trap. 



CHAPTER IX. 

PLUTONIC ROCKS — GRANITE. 

General aspect of granite — Decomposing into spherical 
masses — Rude columnar structure — Analogy and differ- 
ence of volcanic and plutonic formations — Minerals in 
granite, and their arrangement — Graphic and porphyritic 
granite (p. 199.) — Occasional minerals — Syenite — Sye- 
nitic, talcose, and schorly granites — Eurite — Passage of 
granite into trap — Examples near Christiania and in 
Aberdeenshire — Analogy in composition of trachyte and 
granite — Granite veins in Glen Tilt, Cornwall, the Valor- 
sine, and other countries (p. 204.) — Different composition 
of veins from main body of granite — Metalliferous veins 
in strata near their junction with granite (p. 212.) — 
Apparent isolation of nodules of granite — Quartz veins — 
Whether plutonic rocks are ever overlying — Their expo- 
sure at the surface due to denudation (p. 217.) 



CONTENTS. XIU 



CHAPTER X. 

METAMORPHIC ROCKS. 

General character of metamorphic rocks — Gneiss — Horn- 
blende-schist — Mica-schist — Clay-slate (p. 223.) — 
Quartzite — Chlorite-schist — Metamorphic limestone — 
Alphabetical list and explanation of other rocks of this 
family — Origin of the metamorphic strata (p. 226.) — 
Their stratification is real and distinct from cleavage — On 
joints and slaty cleavage (p. 231.) — Supposed causes of 
these structures — how fiir connected with crystalline 
action. 

CHAPTER XL 
METAMORPHIC BOCKS — continued. 

Strata near, some intrusive masses of granite converted into 
rocks identical with different members of the metamorphic 
series — Arguments hence derived as to the nature of 
plutonic action (p. 246.) — Time may enable this action to 
pervade denser masses — From what kinds of sedimentary 
rock each variety of the metamorphic class may be derived 
(p. 252.) — Certain objections to the metamorphic theory 
considered. 



PART 11. 

CHAPTER XII. 

ON THE DIFFERENT AGES OF THE FOUR GREAT CLASSES 

OP ROCKS. 

Aqueous, plutonic, volcanic, and metamorphic rocks, con- 
sidered chronologically — Lehman's division into primitive 
and secondary — Werner's addition of a transition class — 



H\y CONTENTS. 

. ^D^eptupian theory (p. 260.) — Hutton on igneous origin 
of granite — How the name of primary was still retained 
for granite — The term "transition/* why faulty — The 
adherence to the old chronological nomenclature retarded 
the ppo^ess of geology — New hypothesis invented to re- 

. concile the igneous origin of granite to the notion of its 
high antiquity (p. 264.) — Explanation of the chronological 
nomenclature adopted in this work, so far as regards pri- 
mary, secondary, and tertiary periods. 



CHAPTER XHI. 

ON THE DIFFERENT AGES OF THE AQUEOUS ROCKS. 

On the three principal tests of relative age — superposition, 
mineral character, and fossils — Change of ndneral cha- 
racter and fosdlski the same continaoiiB formation — 
Ptoofs that distinct species of animals and plants have 

• lived at suocessive periods — Test of age by included 
fH^gmsots (p. 276.) — Frequent absence of strata of inter- 
vening periods — Principal groups of strata in western 
Europe «-~ Tertiary strata separable into four groups, the 
fossil shells of which approach nearer to those now living 
in propoitioa as the formation is more modern (p. 262.) 
-—Terms Eocene, Miocene, and Pliocene — Identifications 
of fossil and recent shells by M. Deshayes — Opinions of 
Dr. Beck (p. 289.). 

CHAPTER XIV. 

RECENT AND TERTIARY FORMATIONS. 

How to distinguish Recent irom Tertiary strata— Recent and 
Kewer Pliocene strata near Naples-^ near Stockholm and 
Christiania -^ in South Amoica, on coasts of Cfafli and 
Peru ^^ Rodcs of Recent period, wkh IramaB skeleton, in 
Ouadaloupe (p. 296.) — Shells of Uving spedes, with extinct 



CONTEKTS. Xt 

mamnMlia, in loess of the Rhine — Recent •ftid K^er 
Pliocene deposits in Bngland — Older Plioceoe sttntn in 
England — Cfag — Red and Conedline crag •^ thdr featils 
in part distinct (p. 303.) -^ their strata unconformable — 
belong to the same period — London clay (p. 306.) — Its 
shells and fish imply a tropical climate — Tertiary mam- 
malia — Fossil quadrumana. 

CHAPTER XV. 

CRSTACGOUS GROUl*. 

White chalk — Its marine origin shown by fossil shells — 
Rxtinet genera of cephalopoda — Sponges and corals in 
the chalk — ^ No terrestrial or fluviatile sheUs, no land 
plants — Supposed origin of white chalk from deoooiposed 
corals (p. 319.) — Single pebbles, whence derived — ^ Cre- 
taceous coral-reef in Denmark (p. 3S4.) — Maestricfat beds 
and fossils — Origin of flint in chalk — ^Wide area covered 
by chalk (p. 329.) — Green-sand fonnaticHi and fossils — 
Origin of — External configuration of chalk (p. 334«.) — 
Ontstancfing columns or needles •— Period of emergence 
firom the sea — Difference of the chaUt of the north and 
south of Europe— * Hippinites ■«-* Nunmmiites (p. 841 ,) — 
Altered lithological character of cretaceous fomation in 
Spain and Greece — Terminology. 

CHAPTER XVL 

WEALDEN GROUP. 

The Wealden, including the Weald clay, Hastings sand, and 
Purbeck beds — Intercalated between two marine form- 
aitions — Fossil shells fi'eshwater, with a few marine -r- 
Cypris — Fish — Reptiles (p. 349.) — Birds ^ Plains — 
Section showing pass^e of Wealden beneath chalk — 
Junction of Wealden and Oolite — Dirt-bed (p. 3^3.^ — 
Theory of gradual subsidence — Proofs that the Weajden 



XVI CONTENTS. 

fitrafa, notwithstanding their thickness, may*have been 
formed in shallow water (p. 359.) — Geographical extent 
of Wealden — Bray near Beauvais — Relation of the 
Wealden to the Lower Green-sand and Oolite (p. 364.) 

CHAPTER XVII. 

OOLITE AND LIAS. 

Subdivisions of the Oolitic group — Fossil shells — Corals 
in the calcareous divisions only — Buried forest of Encri- 
nites in Bradford clay (p. 373.) — Changes in organic life 
during accumulation of Oolites — Characteristic fossils — 
Signs of neighbouring land and shoals (p. 380.) — Sup- 
posed cetacea in Oolite — Oolite of Yorkshire and Scot^ 
land (p. 384.) 

CHAPTER XVIII. 
OOLITE AND LIAS — continued. 

Mineral character of Lias — Name of Gryphite limestone — 
Fossil fish — Ichthyodorulites — Reptiles of the Lias 
(p. 390.) — Ichthyosaur and Plesiosaur — Newly-disco- 
vered marine Reptile of the Galapagos Islands (p. 394.) — 
Sudden death and burial of fossil animals in Lias — Origin 
of the Oolite and Lias, and of alternating calcareous and 
argillaceous formations (p. 399.) — Physical geography 
(p. 403.) — Vales of clay — Hills and escarpments of lime- 
stone. 

CHAPTER XIX. 

NEW RED SANDSTONE GROUP. 

Distinction between New and Old Red sandstone — Between 
Upper and Lower New Red — Muschelkalk in Germany 
(p. 409.) — Fossil plants and shells of New Red Group, 
entirely different from Lias and Magnesian limestone — 



CONTENTS. XVli 

Lower New Red and Magnesian limestone (p. 413.) — 
Zechstein in Germany of the same age— General resem- 
blance between the oi^ganic remains of the Magnesian 
limestone and Carboniferous strata — Origin of red sand- 
stone and red marl (p. 418.) 

CHAPTER XX. 

THE COAL, OR CARBONIFEROUS GROUP. 

Carboniferous strata in the south-west of England Super- 
position of Coal-measures to Mountain limestone De- 
parture from this type in north of England and Scotland 
— Freshwater strata (p. 423) — Intermixture of fresh- 
water and marine beds — Sauroidal fish — Fossil plants 
(p. 427.) — Ferns and Sigillariae — Lepidodendra — Ca- 
lamites (p. 432.) — Coniferae — Stigmariae. 

CHAPTER XXI. 

CARBONIFEROUS GROUP COWft'wz^erf, AND OLD RED SANDSTONE. 

Corals and shells of the Mountain limestone — Hot climate 
of the Carboniferous period inferred from the marine 
fossils of the Mountain limestone and the plants of the 
Coal (p. 438.) — Origin of the Coal- strata — Contempo- 
raneous freshwater and marine deposits — Modern analogy 

of strata now in progress in and around New Zealanci 

Vertical and oblique position of fossil trees in the Coal 
(p. 444.) — How enveloped — How far they prove a rapid 
rate of deposition — Old Red sandstone (p. 452.) — its 
subdivisions — its fossil shells and fish. 

CHAPTER XXII. 

PRIMARY FOSSILIFEROUS STRATA. 

Primary Fossiiiferous or Transition Strata — Term " Grau- 
wacke" — Silurian Grroup — Upper Silurian and Fossils 



mnn CONTENTS. 

(p«458.) — Lower Siliiriaii and Fo8»il8 -^ Trilofaites 
(p. 46 1 .) ^— Graptqiitef -^ Orthocerato -*^ Occaaioiial ho- 
montality of Silurian Strata — Cambrian Group (p. 464.) 
Bndofi^ptiontte. 

, CHAPTER XXIII. 

ON l-HE DIFFERENT AGES OF THE VOLCANIC ROCKS. 

Tests of relative age of volcanic rocks — Test by si^rpo- 

, sitlon and intrusion — By alteration of rocks in contact — ^ 

, Test by organic remains (p. 47 1 .) — Test of age by mineral 

character — Test by included fragments — Volcanic rocks 

. of the Recent and Newer Pliocene periods (p. 476.) — 

Miocene -^ Eocene — Cretaceous — Oolitic (p. 48 i.) — 

New Red sandstone period — Carboniferous — Old Red 

sandstone period — Silurian — Upper and Lower Cambrian 

periods (p. 485.) — Relative ages of intrusive traps. 

CHAPTER XXIV. 

ON THE DIFFERENT AGES OF THE PLUTONIC ROCKS. 

Difficulty in ascertaining the precise age of a plutonic rock — 
Test of age by relative position — Test by intrusion and 
alteration — Test by mineral composition — Test by in- 
cluded fingments — Recent and Pliocene plutonic rocks, 
why invisible (p. 490.) — Tertiary plutonic rocks in the 
Andes — Granite altering cretaceous rocks (p. 496.) — 
Granite altering Lias in the Alps and in Sky — Granite 
of Dartmoor altering Carboniferous strata — Granite of 
the Old Red sandstone period — Syenite altering Silurian 
strata in Norway (p. 500.) — Blending of the same with 
gneiss — Most ancient plutonic rocks — Granite protruded 
in a solid form (p. 504.) — On the probable age of the 
granite of Arran in Scotland. 



CONTENTS. 



CHAPTER XXV. 

ON TH£ DIFFERENT AGES OF THE METAMQRPHIC AOCXB. 

Age of each set of metamorphic strata twofold (p. 51 L) — 

Test of age by fossils and mineral character not available 

Test by superposition ambiguous — Converaion of dense 
masses of fbssiliferous strata into metamorphic rocks-— 
Limestone and shale of Carrara — Metamorphic strata of 
modem periods in the Alps of Switzerland and Saroy 
(p. 515.) — Why the visible crystalline strata are none of 
them very modem — Order of succession in metamorphic 
rocks (p. 521.) — Uniformity of mineral character — Why 
the metanaorphic strata are less calcareous than the fossili- 
feroQS (p- 52S,). 



Lately published^ 

BY THE SAME AUTHOR, 

Fifth Edition, revised and enlarged, illustrated with 226 Wood- 
cuts, and 16 Plates and Maps, 4 vols. 12mo, 28«. 

PRINCIPLES OF GEOLOGY. 

By Charles Lysll, Esq. ; 

Being an Inquiry how far the former Changes of the Earth's 
Surface are referable to Causes now in Operation ; with a 
GLOSSARY, containing an Explanation of Scientific Terms, 
and a copious Index. 



I * 



ELEMENTS OF GEOLOGY. 



PART L 
CHAPTER I. 

on THE FOUR CTREAT CLASSES OF ROCKS THE AQUEOUS, 

VOLCANIC, PLUTONIC, AND MET AMORPHIC. 

Geology defined — Successive formation of the earth's 
cnist — Classification of rocks according to their origin 
and age — Aqueous rocks. — Their stratification aad ha- 
Mded fossils — Volcanic rocks, with and without cones 
and craters — Plutonic rocks, and their relation to the 
volcanic — Metamorphic rocks, and their probable origin 
— The term primitive, why erroneously applied to the 
crystalline fi>nnations — Division of the work into two 
parts ; the first descriptive of rocks without reference to 
their age, the second treatinjg of their chronology. 

« 

Of what materials is the earth composed, and 
in what manner are these materials arranged? 
These are the inquiries with which Geology is 
occupied, a science which derives its name from 
the Greek yi}, ffe, the earth, and Xoyo^,. hffos, a 
discourse* Such investigations appear, at first 
sight, to relate exclusively to the mineral king^ 
dom, and to the various rocks, soiH and metals, 
^hich occur upon the surface of th6 earth, 'or at 
'Wious depths beneath it* But, in pursuing these 
researches, we soon find ourselves led on to con- 

B 



2 SUCCESSIVE FORMATION OF [Fart t 

sider th^ successive changes which have taken 
place in die former state ;of the •earth's surface 
and interior, and the causes which have given rise 
to these changes ; and, what is still more singular 
and unexpected, we soon become engaged in re- 
searches into the history of the animate creation, 
or of the various tribes of animals and plants 
which have, at different periods of the past, in- 
habited the globe. 

All are aware that the solid parts of the earth 
consist of distinct substances, such as clay, chalk, 
sand, limestone, coal, slate, granite^ and the like ; 
but previously to observation it is commonly 
imagined that all these had remained from the 
first in the state in which we bow see them, — 
that they were created in their present form, and 
in their present position. Geologists have eome 
to a different conclusion. They have discovered 
proofs that the external parts of the earth were 
Xiot all produced in the beginning of tbmgs, in 
the state in which we now bd)old them, nor in 
an instant of time. On the contrary, they ha:ve 
acquired their actual configuration and condition 
gradually, under a great variety of circumstances^ 
and at successive periods, during each of which 
distinct races of living beings have flouridied 
on the land and in the waters, the remains of 
these creatures still lying buried in the crust of 
the earth. 



OlIJ the EAaTH?S CBCffE 8 

By the ^ earth's crnst,^ is meant diat snlall 
pordan of the exterior of our planet vbioh k aor 
cessiUe to iiuman obserra/tion. It comprises not 
merely all of which the structure is laid open hi 
mcmntain prec^ces, or in diK overhanging a 
river or the sea, or whatever the miner may reveal 
in artificial excavations ; but the whole of that 
Duter covering of the planet on which we are 
49iabled to reason by observations made at or near 
the surface* These reasonings may extend to a 
depth of several miles, perhaps ten miles ; but even 
then it may be said, that such a thickness is no 
more than ^^^th part of the distance from the 
sai&oe to the centre. The r-emarlc is just; but 
althonghi the dimensions of such a crust are, in 
truth, insignificant when compared to the entire 
globe, yet they are vast and of magnificent ex- 
lent in relation to man, and to the organic beings 
which people our globe. Referring to this stand- 
iird of magnitude, the geologist may admire the 
ample limits of his domain, and admit, at the 
same tim^ that not only iSie exterior of the 
planet, but the entire earth, is but an atom in 
the midst of the countless worlds surveyed by the 
astronomer. 

Now the materials of this crust are not thrown 
together confusedly, but distinct mineral masses, 
called rocks, are found to occupy definite spaces, 
and to eidiibit a certain order of arrangement. 

B 2 



4 CLASSIFICATION OF BOCK& [Ftttl. 

The term rock is applied indiffewntly by geolo- 
gists to all these substances, whether theybe soft 
or stony, for clay and sand are included in 'the 
term, and some have even brought peat under this 
denomination. Our older writers endeavoured to 
avoid offering such violence to our language, by 
speaking of the component materials of the earth 
as consisting of rocks and soils. But there is 
often so insensible a passage from a soft and inco^ 
herent state to that of stone, that geologists of all 
countries have found it indispensable to have one 
technical term to include both, and in this sense 
we find roche applied in French, rocca in Italian, 
and ^&ar^ in German. The beginner, however, 
must constantly bear in mind, that the term rock 
by no means implies that a mineral mass is in ah 
indurated or stony condition. 

In order to classify the various rocks which 
.compose the earth's crust, it is found most cbn- 
.venient to refer, in the first place, to their origin, 
and in the second to their age. I shall therefore 
begin by endeavouring briefly to explain to the 
student how all rocks may be divided into foiir 
great classes by reference to their different origin, 
<^r, in other words, by reference to the different 
circumstances and causes by which they have been 
produced. 

The first two divisions, which will at: once 
be understood as natural, are the aqueous and 



Ch.IO AQUEOUS B0CK8. 5 

» 

YoLcaniCf or tbe products^ of watery and those et 
igneous Actioa. 

. J^&ua rocks. -^The aqueous rocks, sometimes 
called, tbe sedimentary, or fossiliferouSf caver 
a.lai^er part of the eiarth's sur&ce than any others. 
Hese rocks are stratified, or divided into distinct 
layers, or strata. The term stratum means simply 
abed, or any thing spread out or strewed over a 
given surface; and we infer that the^e strata have 
been generally spread out by the action of water, 
from Vhat we daily see taking place near the 
mouths of rivers, or on the land during temporary 
iojundations. For, whenever a running stream, 
charged with mud . or sand, has its velocity 
checked, as when it enters a lake or sea, or over- 
flows a plain, the sediment, previously held in 
suspension by the motion of the water, sinks, by 
its own gravity, to the bottom. In this manner 
layers of mud and sand are thrown down one 
upon another* 

If we drain a lake which has been fed by a 
small stream, we frequently find at the bottom a 
series of deposits, disposed with considerable re- 
gularity, one above the other; the uppermost, 
perhaps, may be a stratum of peat, next below a 
more dense and solid varie^ of the samp material ; 
still lower a bed of laminated shell-marl, alternating 
^ithpeat or sand, and then other beds of marl, di- 
vided by layers of clay. Now if a second pit be sunlc 

B 3 



2 SUCCESSIVE FORMATION OF CPart I 

sider th^ successive changes which have taken 
place in die former state 'of the >eartfa's surface 
and interior, and the causes which have given rise 
to these changes ; and, what is still more singular 
and unexpected, we soon become engaged in re- 
searches into the history of the animate creation, 
or of the various tribes of animals and plants 
which have, at different periods of the past, in- 
habited the globe. 

All are aware that the solid parts of the earth 
consist of distinct substances, such as clay, chalk, 
sand, limestone, coal, slate, granite^ and the like ; 
but previously to observation it is commonly 
imagined that all these had remained from the 
first in the state in which we how see them, — 
that they were created in their present form, and 
in their present position. Geologists have come 
to a different conclusion. They have discovered 
proofs that the external parts of the earth were 
Xiot all produced in the beginning of things, in 
the state in which we now bdiold them, ikvr in 
an instant of time. On the contrary, they have 
acquired their actual configuration and condition 
gradually, under a great variety of circumstances^ 
and at successive periods, during each of which 
distinct races of living beings have flourished 
on the land and in the waters, the remains of 
these creatures still lying buried in the crust of 
the earth. 



Ch.J.j THE EARTHS CBV8C. 8 

By tbe ^ earth's crnst,'' is xneadt diat snlall 
portion of the exterior of our planet ivliioh k aor 
oessiUe to human obserration. It eomprises not 
merely all of which the structure is laid open hi 
xnouatain precqxices, or in dift overhanging a 
river or the sea, or whatever the jniner may reveal 
in artificial excavations ; but the whole of that 
AUter covering of the planet on which we are 
enabled to reason by observations made at or near 
the sur&oe. These reasonings may extend to a 
depth of several miles, perhaps ten miles ; but even 
then it may be said, that such a thickness is no 
more than ^^jth part of the distance from the 
suriaoe to the centre. The remark is just; but 
although the dimensions of such a crust are, in 
truth, insignificant when compared to the entire 
globe, yet they are vast and of magnificent ex- 
.tent in relation to man, and to the organic beings 
which people our globe. Referring to this stand- 
ard of magnitude, the geologist may admire the 
ample limits of his domain, and admit, at the 
same time, that not only the exterior of the 
planet, but the entire earth, is but an atom in 
the midst of the countless worlds surveyed by the 
astronomer. 

Now the materials of this crust are not thrown 
together confusedly, but distinct mineral masses, 
called rocks, are found to occupy definite spaces, 
*nd to exhibit a certain order of arrangement. 

B 2 



S AQUEOUS ORIGIN OF (Fcit I. 

power to* convey .fine sand or mud into the.sea. 
Hence^ alternate layers of gravel and fine sedi- 
ment aecumulate under water, and such alter- 
nations are found by geologists in the interior of 
every continent* * 

If. a stratified arrangement, and the rounded 
forms of pebbles, are alone sufficient to lead 
us to the conclusion that certain rocks origin- 
ated under water, this opinion is farther con- 
firmed by the distinct and independent evidence 
oi fossilsi so abundantly included in the earth's 
crusL By a fossil . is meant any body, or the 
traces of the existence of any body, whether ani- 
mal or vegetable, which has been buried in the 
earth by natural causes. Now the remains of 
animals, especially of aquatic species, are found 
almost everywhere imbedded in stratified rocks. 
Shells and corals are the most frequent, and with 
them are often associated the bones and teeth -^ 
fish, fragments of wood, impressions of leaves, and 
other organic substances. Fossil shells of forms 
duch as now abound in the sea, are met with fiir 
inland, both near the surface and at all depths 
below it, as far as the miner can penetrate. They 
occiir at all heights above the level of the ocean, 
having be«i observed at an elevation of from 
8000 to 9000 feiet in the Alps and Pyrenees, more 

' * See Principles of Geology by the author ; refer to * Mag- 
nan/ and ' Conglomerates/ in the Index of different editions. 



OlL] certain rocks. 9 

than 13,000 feet high in the Andes, and above 
15,000 feet in the Himalayas. 

These' shells belong mostly to marine testacea, 
but in some places exclusively to forms character- 
istic of lakes and rivers. Hence we conclude that 
some ancient strata were deposited at the bottom 
of the sea, while odiers were formed in lakes and 
estuaries. 

When geology was first cultivated it was a 

general belief, that these marine shells and other 

* 

fossils were the effects and proofs of the general 
deluge. But all who have carefully investigated 
the phenomena have long rejected this doctrine. 
A transient flood might be supposed to leave 
behind it, here and there upon the surface, 
scattered heaps of mud, sand, and shingle, with 
shells confusedly intermixed ; but the strata con- 
taining fossils are not superficial deposits, and do 
not cover the earth, but constitute the entire mass 
of mountains. It has been also the favourite notion 
of some modem writers, who are aware that fossil 
bodies cannot all be referred to the deluge, that 
they, and the strata in- which they are entombed, 
may have been deposited in the bed of the ocean 
during a period of several thousand years which 
intervened between the creation of man and the 
deluge. They imagine that the antediluvian bed 
of the ocean, after having been the receptacle of 
matfy stratified deposits, became convierted, at the 

B 5 



10 AQXTEOVS ROCX& tP«tL 

time of the flood, into the lands ^ich we itihabit^ 
and that the ancient continents were at the sslvM 
time sttbmergedy and became the bed of the 
present sea* This hypothesis, however preferable 
to the diluTial theory, as admitting that all 
foBsiliferous strata were slowly and sncoeflsively 
thrown down from water, is yet wholly inadequate 
to explain the repeated revolutions which the eardi 
has undergone, and the signs which the existing 
continents exhibit, in most regions, of having 
emerged from the ocean at an era far more remote 
than four thousand years from the present time^ 
It will also be seen in the sequel, that many 
distinct sets of sedimentary strata, each several 
hundreds or thousands of feet thick, are piled one 
upon the other in the earth's crust, each con- 
taining their peculiar fossil animals and plants, 
which are distinguishable with few exceptions 
from species- now living. The mass <>f some of 
these strata consists almost entirely of corals, others 
ire made up of shells, others of plants turned 
into coal, while some are without fossils. In one 
9iet of strata the species of fossils are marine^ 
in another, placed immediately above or bdow^ 
they as clearly prove that the d^osit was fbrmed 
in an estuary or lake. When the student has 
more fully examined into these appearances^ he 
will become convinced that the time required for 
ifae origin of the actual continents must have been 



OuL] VOLCAHIC SOCK&' II' 

&r greater than that which it ecmceded by the 
theory above alladed to, and that no one uniyenal 
and sudden conTersion of sea into land will account 
for geological appearances. 

We have now pointed out one great class of 
rocks, which, however they may vary in mineral 
composition, colour, grain, or other characters, 
external and internal, may nevertheless be grouped 
together as having a common origin. They 
have all been formed under water, in the same 
manner as sand, mud, shingle, banks of shells, 
coral, and the like^ and are characterized by stra* 
tification or fossils, or by both. 

Volcanic roeks^r^ The division of rocks which we 
may next consider are the volcanic, or those which 
have been produced, whether in ancient or modern 
times, not by water, but by the action of fire, or 
subterranean beat, lliese rocks are for the most 
part unstratified, and are devoid of fossils. They 
are more partially distributed tlian aqueous form- 
ations, at least in respect to horizontal extension* 
Among those parts of Eui*ope where they exhibit 
diaraeters not to be mistaken, I may mention not 
only Sicily and the country round Naples, but 
Auv^gne, Velay, and Vivarais, now the de* 
partments of Puy de Dome, Haute Loire, and 
Ardeche, towards the centre and south of France, 
in which we find several hundred conical hills 
haying the forms of modern volcanos, with craters 

B 6 



\2 VOLCAXIC (NftlGXN QPart I^' 

mo]:e or less perfect on many of their .summits* 
These cones, are composed moreover of lava, saud, 
and asheS) simitar to. those of active, Tokanos. 
Streams of lava may sometimes be tiraeed proceed-* 
ing from the ,cones into the adjoining valleys, 
where they choke up. the ancient channels of rivers 
with solid rodC} in the* same. manner as some 
modern flows of lava in Iceland have been known 
to do, the rivers either flowing beneath or .cutting 
out a narrow passage on one side, of the laya* 
Although none of these French voleanos have be^n 
in activity within the periodof history or tradition, 
their forms are often very perfect. . Some how- 
ever have been compared . to the mere skeletons 
of voleanos, the rains and torrents having washed 
their sides, and removed all the loose sand and 
scories, leaving only the harder and more solid 
materials. By this erosion, and by earthquakes^ 
their internal structure has occasionally been laid 
open to viQW, in fissures and ravines ; and we then 
behold not only many succes^ve beds and masses 
of porous lava, sand, and scoriae^ but also per- 
pendicular walls, or dikesy as they are called,, of 
volcanic rock,, cutting through the other materials. 
Such. dikes are. also observed in the structure, of 
Vesuvius, Etna, and other active voleanos. They 
have, been formed by the pouring of melted 
matter, whetlier from above or below, into open 
^sures, and they commonly traverse, deposits.of 
volcanic tuffy a substance produced by the shower- 



Ch.M OV ABSTAIN BOCKa 13 

kg down from the air, or incumbent wsten^ of 
sand and cinders, first shot up firom the interior 
of the earth, by explosions of volcanic gases* > 

Besides the parts of France above alluded 
to, there are other countries, as the north of 
Spain, the south of Sicily, the Tuscan territory of 
Italy, the lower Rhenish provinces, and Hungary^ 
where spent volcanos may be seen with cones, 
craters, and often accompanying lava-streams. 

There are also other . rocks in England, Scot« 
land, Ireland, and almost every country in Europe, 
which we infer to be of igneous origin, although 
they do not form hills with cones and craters. 
Thus, for example, we feel assured that the rock 
of Stafia, and that of the Giants' Causeway, 
called basalt, is volcanic, because it agrees in its 
colunuiar structure and mineral composition with 
streams of lava which we know to have flowed 
from the craters of volcanos. We find also 
similar basaltic rocks associated with beds of tv^ff 
in various parts of the British Isles, and fcnrming 
ixhes^ such as have been spoken of ; and some of 
the strata through which these dikes cut are'occar 
sionally altered at the point of contact, as if they 
had been exposed to the intense heat of melted 
matter. 

The absence of cones and craters, and long 
narrow streams of lava, in England and elsewhere, 
is principally attributed by geologists, to the erup- 
tions having been formerly submarine, just as a 



14 FLUVONIC aOGKS [Paitl. 

oonodeiable propordoii of Tcdoanoa in onr own 
tunes burst oat beneath the set. But this queatioiL 
must be enlarged upon more fully in the dk^qpters 
on Igneous Rocks> in which it will alao be shewn, 
that as di£ferent sedimentary formatkms, contaiii-! 
ing each their characteristic fossilst have been de- 
posited at successive periods, so also Yolcanic s«id 
and scoriae have been thrown out, and lavas have 
flowed over the land or bed of the sea, at many 
different epochs, or have been injected into 
fissures ; so that the igneous as well as the aqueous 
rocks may be classed as a chronological series of 
monuments, throwing light on a suocessioo of 
events in the history of the earth. 

PbUonic rocks.^ We have now therefore pointed 
out the existence of two distinct orders of mineral 
masses, the aqueous and the volcanic: but; if we 
examine a large portion of a continent, especially 
if it ocmtain within it a lofty mountain range^ we 
rarely fail to discover two other classes of rocks, 
very distinct ttom either of Uiose above alluded to, 
and whidi we can neither assimilate to deposits 
such as are now accumulated in lakes or seas, nor to 
those gaoerated by onUnary volcanic action. The 
members of both these divisioaas of rocks s^ee in 
being highly crystalline and destitute of organic 
remains. The rodcs of one division have been 
called plutonic, comprehending all the granites 
and certain porphyries, which are nearly allied in 



Cb. L] AHD THBIB OBIOIK. |5 

some of their tfaaracters to volamic formatioiit. 
Tbe members of the other clafls are etratified end 
often tlatj, and have been called by aome the cryt- 
taUme scJdstg. In these are included fpetm^ nu^ 
caoecms^ediist (or mica«slate)» hornblende-schist^ 
statuaty marble, the finer kinds of roofing slatei 
and other rocks afterwards to be described^ 

As it is admitted that nothing strictly analogous 
to these crystalline producti<Nis can now be seen in 
tbe progress of formation on the earth's surface, it 
will naturally be asked, on what data we can find a 
place for them in a system of classification founded 
on the origin of rodra« First then, in regard to 
the plutonic class^ a passage has been traced firom 
rarious kinds of granite into different varieties of 
iwks decidedly volcanic ; so that if the latter are 
of igneous origin, it is scarcely possible to refuse 
to admit that the granites are so likewise. Second* 
ly, large masses of granite are found to send forth 
dikes and veins into the contiguous strata, very 
much in the same way as lava and volcanic matMr 
penetrate aqueous deposits, both the massive g^a« 
nite and tlie veins causing dianges analogous to 
those which lava and volcanic gases are known 
to produce. But the plutonic rodcs difier from 
the volcanic, not only by their more crystalline 
texture^ but also by the absence of tui& and 
breccias, which are the products of eruptions at 
the earth's surfece. They differ also by the abs^ce 



16 PLUTONIC BOCKS. CPutL 

of pores or cellular cavities, which the entangled 
gases give rise to in ordinary lava. From these 
and other peculiarities it has been inferred, that 
the granites have been formed at great depths in 
the eartli, and have cooled and crystallized slowly 
under enormous pressure where the contained 
gases could not expand. The volcanic rocks, on 
the contrary, although they also have risen up from 
below, have cooled from a melted state more rapidly 
upon or near the surface. From this hypothesis 
of the great depth at which the granites origi- 
nated, has been derived the name of <' Plutonic 
rocks," which they have received to distinguish 
them from the volcanic. The beginner will easily 
conceive that the influence of subterranean heat 
may extend downwards from the crater of every 
active volcano to a great depth below, perhaps 
several nul^ or leagues (see Frontispiece), and 
the effects which are produced deep in the bowels 
of the earth may, or rather must be distinct ; so 
that volcanic and plutonic rocks, each di£Perent in 
texture, and sometimes even in composition, may 
originate simultaneously, the one at the surface, 
the other far beneath it. 

Although granite has often pierced through 
Other strata, it has rarely, if ever, been observed 
to rest upon them as if it had overflowed. But 
as this is continually the case with the volcanic 
rocks, they .have been slyled from this pecu- 



Cb.J.J HETAMORPHIC ROCK8. 17 

liarit]r». ^^ overlying '* bj Dr. MacCulloch; and 
Mr. Necker has proposed, the term << underlying" 
for the granites, to designate the opposite mode in 
which they almost invariably present. themselves* 
Metanwrphic rocks. — The fourth and last great 
division of rocks are the crystalline strata or schists, 
called gneiss, mica-schist, clay-slate, chlorite* 
schist,. marble, and the like, the origin of which 
is more doubtful than that of the other three 
classes. They contain no pebbles or sand or 
scorias, or angular pieces of imbedded stone, and 
no traces of organic bodies, and they 4re often as 
crystalline as granite, yet are divided into beds, 
corresponding in form to those of sedimentary 
formations, and are therefore said to be stratified. 
The beds sometimes consist of an alternation of 
substances varying in colour, composition, and 
thickness, precisely as we see in stratified fossi- 
liferous deposits. According to. the theory, which 
I adopt as most probable, and which will be 
afterwards more fully explained, the malscials 
of these strata were originally deposited from 
water in the usual form of pediment, but they 
were subsequently altered by subterranean heat, 
so as to .assume a new texture. It is demon- 
strable, in some cases at least, that such a complete 
conversion has actually taken place. I have al- 
ready remarked that alterations, such as might 
be produced by intense heat, are observed in strata 



18 XETAVOSFBIGr ROCKS [ftttt I. 

tear dieir conitact with veins and dikes* of volcsmo 
rockff. These, howevet, are on a SBEiall^cate; but 
&8iinilflur inftrence has been exerted asueh nove 
pow^n^iy in the neigUbourfaood of plalonie vocks 
nnder different cireumstanee% and perhaps . in 
combination with other causes. The efleots there- 
by siqperinduced on fossiliferovs strata hare some* 
times extended to a distance of a quarter of a 
mile from the point of contact. Throughout the 
goeater part of this space the fossiiiferous beds 
hxve exchanged an earthy for a h%hly crystalline 
texture, and haye lost all traces of organic remains^ 
Thus, for example, dark limestones, replete with 
shells and corals^ are turned into white 'statuctry 
marble, and hard clays into slates called mica- 
schist and hornblendeHu^his^ all signs of organic 
bodies having been obliterated. 

Although we are in a great degree ignorant of 
the precise nature of the influenee here exerted, 
yet it evidently bears some analogy to that which 
volcsmic heat and gases are capable of producing; 
and the action may be conveniently called plu-* 
tonic, because it appears to have been developed 
in those regions where plutonic rocks are gene* 
rated, and under similar circumstances of pressure 
and d^th in the earth. Whether electricity or 
any other causes have co-operated with heat to 
produce this influence^ may be matter of specu^ 
latioo, but the plutonic inflneiMe has sometimes 
pervaded entire mountain masses of strata. The 



phenQsnena* tlierefon^ being soiaetimes on Mm 
gr^nd a scak^ we most not couider tbat die 
stvala have 9ikw9j9 assuaied their erystallme or 
altered textnre m consequence of the proxhnitj 
of granitie^ bat radwr that granite itself, as weH aa 
the altered strata^ have derived their crystallitie 
texture from phitonic agency. 

In accordance with this hypothesis I have pro- 
posed (see Principles of Geology), the term 
'^ Metamorphic " for the altered strata, a term 
derived from /Krera, meta, trmns^ and /K.opf i}, morphe, 
^^rww5. 

Hence there are are four great classes of rocks 
considered in reference to their origin, —* the 
aqueous, vc^eanic, plutonic, and metamorphic, all 
of which may be ccmc^ved to have been formed 
contemporaneously at every geological period, and 
to be now in the progress of formation. By refer- 
ring to the Fnmtispiece, the reader will perceive 
what relative positions the members of these four 
great classes A, B, C, I>, may occupy in the 
earth's crust, while in the course of simultaneous 
production. Thus, while the aqueous deposits A, 
which are expressed by the yellow colour, have 
been accumulating in successive strata at the bot- 
tom of the sea, the volcanic cone B, has been 
piled up during a long series of eruptions, and the 
other igneonB rocks coloured purple have also 
aaeended ftcm bdlow in a fluid state. Some of 



SQ CONTBHTDRANEIRJFa ORIflTTK OF [Firt I. 

tbesB lasl have been poured forth into the sea^ 
amd there mingled with : aqueous sediment On 
piursuing • downwards either the small dikes- or 
large masses of volcanic rock, we find them pass 
gradually into plytonic formations, D, which are 
c<^ured red, and which underlie all the rest« 
These last again are seen to be in contact with 
a zone of contemporaneous inetamorphic strata, 
C, coloured blue, which they penetrate in nu- 
merous veins. 

In that part of the sectipn which is uncoloured, 
a more ancient series of mineral masses are seen, 
belonging also to the four great divisions of rocks. 
The strata from a to i represent as many dis- 
tinct aqueous formations, which have originated 
at different periods, aiid are each distinguished by 
their peculiar fossils. The mass t> t? is of volcanic 
origin, and .was formed at one of those periods, 
namely, when the strata ff were deposited. The 
strata m m are ancient metamorphic formations, 
and the rocks 1, 2, are plutonic, also ancient, but 
of diiFerent dates. 

, Now it will be shewn in the course of this 
volume^ that portions of each of these four distinct 
classes of rocks have originated at many succes- 
sive periods. It is not true, as was formerly sup- 
posed, that all granite, together with the crystal- 
line or metamorphic strata, were first formed, and 
therefore entitled to be called ^^ primitive," and 



Ch. 1.1^ FOU& CIsASgm OF JtOCK& _ 2] 

that the aqueous aiid volcanic roeka were aftei^- 
wards superimposed, and should, therefore^ rank 
as secondary in the order of tune. This idea was 
adopted in the infancy of the science, when aH 
fiMrmatifCMis, whether stratified or unstratifitd) 
earthy or crystalline, with or without fossils, were 
alike regarded as of aqueous origin. At that 
period it was naturally argued, that the foundation 
mu^t be older than the superstructure. Granite 
as being the lowest rock, must have been first 
" precipitated from the waters of the primeval 
ocean which originally invested the globe," then 
the crystaUine, and finally the fossiliferous strata, 
together with other associated rocks, were de^ 
posited. 

But when the doctrine of the igneous origin of 
granite was generally adopted, the terms primi- 
tive and primary, as embracing the plutonic and 
metamorphic rocks, should at once have been 
banished from the nomenclature of geology. For 
after it had been first proved that granite had 
originated at many difierent epochs, some ante*- 
cedent, others subsequent to the origin of many 
fossiliferous strata, it was also demonstrated that 
strata which had once contained fossils, had be*- 
come metamorphic at difierent periods ; in other 
words^ some of the rocks termed primary were 
newer than others which were called secondary. 
A question^ therefore, has arisen^ whether the 



22 COmOSKFOSAMlOinS OSimN of. IFtutl. 

hmer crystallihe portiotra of the earth's crust, {nov 
£mBv modified as they ha^e heed^ and renewed 
from time to diae, aire neii^r or older, regarded 
as « whole, than due sedimentary and volcaine 
formations* Have lite operations ^f decsgr and 
repair been nmst active ahore or helow? The 
Bame question might be asked with respect to tihe 
tfdatiye antiqnifty of the foundations and the build*- 
higs in certain.ancient cities, such ae Venice or Am*- 
jMerdam, which are supported on wooden piles— 
whether in thfe cotirse of ages hare the wooden 
props, or the buildings of brick, stone, and mar- 
ble which they support, proved the most durable ? 
Which have been renewed most frequently ? for 
the piles, when rotten, can be removed one after 
the other without injury to the buildings above. In 
like manner the materials of the lower part of 
the earth's crust may pass from a solid to a fluid 
state, and may then again become consolidated; 
or sedimentary strata may assumie a new and 
metamorphic texture, while the strata abave con- 
tinue unchanged, or retain characters by whidi 
their claim to high antiquity may be recognized. 
During such subterranean mutations, the earth- 
quake may shatter and dislocate the incumbent 
crust, or the ground may rise or sink slowly and 
insensibly throughout wide areas * ; or there may 

* See chap. 5. 



Ck.1^ IFOVM C9LA48BB OP BOCKS. 

be, volcanic eruptions here and liiere; but ibe 
gxea$, Bia9s may xuH iiiiderga svidi an alteratm 
as to be regenerated and oomposed of new rocks. 
As all t^e ctrydtaUine rocks niayt in iMWie re- 
fii|)ects, be viewed as belonging to one great fiuEidlyv 
whether they be stratified or nnstratifiedf it wiU 
G&eEL be eonv^iient to i^edk of theia by one conii* 
mon name. But the use of the term primary 
wouHd imply a. manifest contradiction^ few reasons 
which the student will now comprehend* It is 
indispensable, therefore, to find a new name» one 
which must not be of chronological import, and 
must, express, on the one hand, some peculiarity 
equally attributable to granite and gneiss (to the 
plutonic as well as the altered rocks), and, on the 
other, must have reference to characters in which 
those rocks differ, both from the volcanic and 
£*om the unaltered sedimentary strata. I have 
proposed in the Principles of Geology the term 
'^ hypogene '' for this purpose, derived from (mo^ 
vnder, and yivofLai^ to be bom ; a word implying 
the theory that granite,. gneiss, and the other crysr 
talline formations are alike nether-formed vof^^^ or 
rocks which have not assumed their present form 
and stiiicture at the surface. It is true that all meta- 
morphic strata must have been deposited originally 
at the surface, or on that part of the exterior of 
the globe which is covered by water ; but, accord- 
ing to the views above set forth, they could never 



J24 DIVISION OF THE WOBKI [Put L 

have acquired their crystalline texture, linle^ 
lliey had been modified by plutonic agency under 
pressure in the depths of the earth. 

Fi*om what has now been said, the reader will 
understand that the four great cla3ses of rocte 
may each be studied under two distinct points of 
view : first, they may be studied simply as mineral 
masses deriving their origin fcota particular causes, 
and having a certain composition, form, and po^ 
sition in the earth's crust, or Other characters both 
positive and negative, such as the presence or 
absence of organic remains. In the second placef, 
the rocks of each class may be viewed as a grand 
chronological series of monuments, attesting a suc^ 
cession of events in the former history of the globe 
and its living inhabitants. 

I shall accordingly divide this work into two 
parts, in reference to these two modes of consider- 
ing each family of rocks. In the first part, the 
characters of the aqueous, volcanic, plutonic, and 
m^tamorphic rocks will be described, without 
reference to their ages, or the periods when they 
were formed. In the second, their difierent ages 
will be considered, and I shall endeavour to ex- 
plain the rules according to which the chronology 
of rocks in each of the four classes may be de- 
termined. 



25 



CHAPTER 11. 

AaVEOUS BOCKS — THBIR COMPOSITION AND FORMS OP 

STRATIFICATION. 

Minenil composition of strata — Arenaceous rocks — Ai]giU 
laceous — Calcareous — Gypsum — Forms of stratification 
— Original horizontality — thinning out — Diagonal ar- 
raogeinent — Ripple mark. 

First, then, in pursuance of the arrangement 
explained in the last chapter, we have to examine 
the aqueous or sedimentary rocks, which are for 
the most part distinctly stratified, and contain 
fossils. We are to consider them with reference 
to their mineral composition, external appearance, 
position, mode of origin, and other characters 
which belong to them as aqueous formations, 
without reference to their age, or the various 
geological periods when they may have origi- 
nated. 

I have already given an outline of the data 
which lead to the belief that the stratified and 
fossiliferous rocks were originally deposited under 
water; but, before entering into a more detailed 
investigation, it will be desirable to say something 
of the ordinary materials of which such strata 
are composed. These may be said to belong 
principally to three divisions, the arenaceous, the 
argillaceous, and the calcareous which are formed 

c 



26 MIKERAL ^IMPOSITION [Parti. 

respectively of sand, clay, and carbonate of lime. 
Of these, the arenaceous, or sandy masses, are 
chiefly made up of siliceous or flinty grains ; the 
argillaceous, or clayey, of a mixture of siliceous 
matter, with a certain proportion, about a fourth 
in weight, of aluminous earth ; and, lastly, the 
calcareous rocks or limestones consist of carbonic 
acid and lime. 

Arenaceous or siliceotis rocks. — To speak first of 
the sandy division: beds of loose sand are frcv 
quently met with, of which the grains consist eii«> 
tirely of silex, which term comprehends all purely 
siliceous minerals, as quartz and common flint. 
Quartz is silex in its purest form; flint usually, 
contains some admixture of alumine and oxide of 
iron. The siliceous grains in sand and sandstone 
are usually rounded, as if by. the action of running 
water; but they sometimes, though more rarely^ 
consist of small crystals, as if they had been che- 
mically precipitated from a fluid containing silex 
in solution-. 

Sandstone is an aggregate of such grains, which 
often cohere together without any visible cement^ 
but more commonly are bound together by aslight 
quantity of siliceous or calcareous matter, or by 
iron or clay. In nature there is every intermediate 
gradation, from perfectly loose sand, to the hard- 
est sandstone. In micaceous sandstone mica is 
abundant; and the thin silvery plates into which 



ClLl£a:. ^ SSV^TIFIED BOCMB, ^^ 

tiiat muiend jdivid^B% aro arn^god ittJ^ifnh 
parallel .tcr the planes of stratifieatiooy ffri^g a> 
slatjr or Jamiilated textove to the rock. > 

When sandstone is coarse^gramedy it is aaoidtjr.' 
called £^ If the grains, are ronndedy and iai|^ 
eaongh to be called pebbles, it becomes a 4sanyfe* 
mer^ or piukHf^-stom^ which may consist c^- 
pieces of one or of many different kinds of roekv- 
A.coQ^omerate, ther^re, is simply gravel boimd 
together by a cement 

ArgiUaceous rocks. -*^ Clays strictly speaking, is a 
mixture of silex* or flint with a large proporti<MV 
usually about one fourth,. of the substance called^ 
alamine;, or argil;, but,, in commcMi langu^e, any .. 
earth whieh possesses sufficient ductility^ vh^ 
kneaded iip wjtb water, tobe faahioBed like paate* 
bj the hand^ or by the potter's ladle,, is called it 
day;, and such clays vary greatly in) their coin**; 
position^ and' are, in general, nothing, more thai;i^ 
mud derived firom the decomposition or wearing 
down of various' rocks. The purest clay foundin* 
nature is porcelain day, or kaolin, which xesuks 
frcHn the decomposition of a rock composed o^ 
felq^ and quartz, and it is almost always . mixed 
widi quartz.* ^ude has also the property, like 

* The kaolin of China consists of 7 rid parts of siles, 
15-86 of aiumine, 1*92 of lime, and 6*73 of water, (W.Phil- 
lips, Mineralogy, p. 33.) ; but other porcelain clays differ 
materially, that of Cornwall being composed of 60 parts 
of alumiiie and 40 of silex. (Ibid.) 

C 2 



3Q XINGRAL COMPOSITiaN CVtttt 

d^y^ of becoming plastic in water : it is a more 
fiolid form of clay, having been probably <^u- 
densed by pressure. It usually dividi^ into thin 

lamioffi- 

• One general character of all argillaceous rocks 
is to give out a peculiar pdour when breathed 
upon, which is a test of the presejKe of alumine, 
akbough it does not belong to pure alumine, but, 
apparently, to the combination of that substance 
with oxide of iron. * 

Cateareotts rocks. — This division comprehends 
those rocks which, like chalk, are composed of 
lime and carbonic acid. Shells and corals are 
also formed of the same elements, with the addition 
of animal matter. To obtain pure lime it is 
necessary to calcine these calcareous substances, 
that is to say, to expose them to heat of sufficient 
intensity to drive off the carbonic acid, and other 
volatile matter, without vitrifying or melting the 
lime itself. White chalk is often pure carbonate 
of lime ; and this rock, aldiough usually in a soft 
and eartby state, is sometimes sufficiently solid to 
be used . for buikling, and even passes into a 
emryxict stone, or a stone of which the separate 
(mixCs. are so minute as not to be distinguishable 
frdin eiBMjh other by the naked eye. 

• Many limestooes are made up entirely of rainute 

# See W. Phillips's Mineralogy, " Alumine.** 



Ch.IL3 OF 9TBATIP1ED ROCK& 26 

iragments of shells and coral, or of calcareous 
sand cemented together. These last might be 
called ^< calcareous sandstones ; ^ but that term 
is more properly applied to a rock in which 
the grains are partly calcareous and partly 
siliceous, or to quartzose sandstones, having a 
cement of carbonate of lime. 

The variety of limestone called " oolite '* is com- 
posed of numerous small egg-like grains, resem- 
bling the roe of a fish, each of which has usually a 
small fragment of sand as a nucleus, around which 
concentric layers of calcareous matter have accu- 
mulated. 

Any limestone which is sufficiently hard to take 
a fine polish is called marble. Many of these are 
fossiliferous ; but statuary marble, which is also 
called saccharine limestone, as having a texture 
resembling that of loaf-sugar, is devoid of fossils, 
and a member of the metamorphic series. 

Siliceous limestone is an intimate mixture of 
carbonate of lime and flint, and is harder in pro- 
portion as the flinty matter predominates. 

The presence of carbonate of lime in a rock may 

be ascertained by applying to the surface a small 

drop of diluted sulphuric, nitric, or muriatic acids ; 

for the lime, having a stronger chemical affinity 

for any one of these acids than for the carbonic, 

unites itself immediately with them to form new 

c 8 



'cdmpOiQndd, thereby becoming a suljibatey nhtatey 
or muriate of lime. The carbonic ackJi when iJHis 

' Uberated from its Ujiuon with th^ lime, escaqpes in 
a gaseous form, and froths up or e&rvesces as it 
makes its way in small bubbles through the drop 
of liquid. This efiervesoenee is brisk or feeble in 
proportion as the limestone is pure or impure, or, 
in other words, according to the quantity of foreign 
matter mixed with the carbonate of lime. Witbr 
put the aid of th^ test, the most experienced 
eye cannot ^ways detect the presence of lime 'm 
rocks. 

The above-mentioned three classes of rocks, 
tlie arenaceous, argUJaceous, and Qaleareoi9S, pass 
contijjiualiy into each other, a^d rarely ooouir in 
a perfectly separate and pure form. Thus it 
is an exception to the ^neral rule to meet 
with a limestone as pure £^ prdiparf white chalk, 
or with clay as aluminous as th^it psed in 
Cornwall for porcdaiii, or with sand 30 lentirely 
composed of siliceous gr^dns as the white saiid of 
Alum Bay in the Isle of Wjg^t, or sandstone so 
pure as the grit of Font;ajjaebl^au, used for pave- 
ment in France. More coim^npnly we find sauad 
and clay, or clay and marl, intermi?:ed in lii^ same 
mass. When the sand and day are each in con- 
siderable quantity, the mixture js called loam. If 
there is much calcareous matter in cliKy it isx^Ued 
marl; but this term has unfortunately been used 



Ch.IXJ or STRATIFIED BOCK& ' SI 

80 vaguely, as often te be very ambigaous. It has 
heefn appUed to substances in which there is bo 
lime; as, to that red loam usually called red marl 
in certain p^ts of England. Agriculturists were 
in the habit of doling any soil a marl, which, like 
true marl, fell to pieces readily on exposure to the 
air. Hence arose the confusion of using this 
name fer soils which, con»sting of loam, were 
eaaly worked by the plough, though devoid of 
Erne. 

Marl dabs bears the same relation to marl which 
shale bears to day, being a calcareous shale. It 
is vei^ abundant in some countries, as in the 
Swiss Alps. Argillaceous or marly limestone is 
also of common occurrence. 

There are few other kinds of rock whicli enter 
solai^elyinto die composition of sedimentary strata 
as to make it necessary to dwell here on their 
characters. I may, however, mention two others, 
' — magnesian limestone or dolomite, and gypsum. 
Magtiesian limegtom is composed of carbonate of 
Ikne and carbonate of magnesia : the prc^rtion of 
the latter amounting in some cases to nearly one 
half. It effervesces much more slowly and feebly 
with acids than coramoii limestone. In England 
this rock is generally of a yellowish coloiur; but it 
varies greatly in mineralogical character, passing 
from an eartiiy state to a white compact stone of 
great hardness. Dolomite^ so common in many 

c 4 



82 FORMS OF STBATIFICATIOK. tf**th 

parts of Germaqji: and F^pcu^^ ifi |i)go a^varielf 
of magnesiaq limestone, .usually .of a -graHnlar 
texture. . i 

Gypsum* — Gypsum is. a rock coioposed of aul- 
pjburic acid, lime, and wat^r. It. is ji8i«aUy a soft 
whitish-yellow rock, with a texture resembling 
that of loaf-sugar, but sometimes it is entirely 
composed of lenticular crystals. It is insoluble 
in acids, and does not effervesce like chalk and 
dolomite, the lime being already combined with 
sulphuric acid, for which it has a stronger affinity 
than for any other* Anhydrous gypsum is a rare 
variety, into which water does not enter as a com-r 
ponent part. Gypseous marl is a mixture of 
gypsum and marl. 

Forms of strati/kation. — A series of sti'ata 
sometimes consists of one of the above rocksj 
sometimes of two or more in alternating beds. 
Thus, in the coal districts of England, for example, 
we often pass through several beds of sandstone, 
some of finer, others of coarser grain, some white, 
others of a dark colour, and below these, layers of 
shale and sandstone or beds of shale, divisible into 
leaf-like laminae, and containing beautiful impres- 
sions of plants. Then again we. meet with beds of 
pure and impure coal, alternating with shales, and 
underneath the whole, perhaps, are calcareous 
strata, or beds of limestone,, filled with corals and 
marine shells, each bed distinguishable from an- 



dtll] ALISBMATIONS. "" ^ 

oflidHVj^dirti^ifl ifasstb, or by die abund^ce ^o? 
i;i6^H»a» fip^es of 'sbdld or zoophytes/ ^ ' '' 

This altemalion of different kinds of rock pn>- 
dne^s'dife most distinct stratification ; luid we often 
fi^d beds of limestone and marl, conglomerate and^ 
sM^tstcfoi^,' saddahd clay, recurring again and 
Bf^^ih ifeariy^ regular order, throughout a series 
rf^riiatiy^ hundred strata. The causes which may 
[M'oduc^e these phenomena are various, and have 
been folly discussed in my treatise on the modem 
changes of the earth's surface. * It is there seen 
that rivers flowing into lakes and seas are charged 
with sedinient, varying in quantity, composition, 
colour, and grain according to the seasons ; the ' 
waters are sometimes flooded and rapid, at ' 
other periods low and feeble ; different tributaries, 
also, draining peculiar countries and soils, and 
therefore charged with peculiar sediment, are 
swollen at distinct periods. It was also shewn 
that the waves of the sea and currents undermine 
thediflfe during wintry storms, and sweep away 
the mateiials into the deep, afler which a season ^ 
of tranquillity succeeds, when nothing but* tlie 
&iest mud is spread by the movements of the 
oeean over the same submarine ariea. 

It \9 not the object of the present work to give * 
a dei^cripljon of these operations, repeated as they 

• Consult Index to Prin. of Geol « Stratjific^fl^' " C}«s;rt 
renti,^ deltas,*' **»^ Water,* &c. 

c 5 



'axe, year aift^ year, and cealufy after cestiDdy $ bat 
* 1 may suggest an exfdaaation of the manner in 
wMch some micaceous sandstones hare originated, 
those in which we see innumerable thin layers of 
mica dividing layers of fine quartzose sand. I chr 
served the same arrangement of materials in recent 
mud deposited in the estuary of La Roche St Ber- 
nard in Brittany, at the mouth of the Loire. The 
surrounding rocks are of gneiss, which, by its 
waste, supplies llie mud : when this dries at low 
water, it is found to consist of brown laminated 
day, divided by thin seams of mica. The sepa- 
ration of the mica in this case, or in that of 
micaceous sandstones, may be thus understood. 
If we take a handful of quartzose sand, mixed 
with mica, and throw it into a clear running 
streamt we see the materials immediately sorted 
by the water, the grains of quartz fiJling almost 
directly to the bottom, while the plates of mica 
take a much longer time to reach the bottom^ and 
are earned farther down tbe stream. At the first 
instant the water is turbid, but immediately after 
the flat sur&ces of the plates of mica are seen alone 
reflectmg a silvery light, and tbey descend slowly, 
to form a distinct micaceous lamina. The mica is 
the heavier mineral of the two; but it remains 
longer suspended, owing to its great es^te&t <^ sur- 
face. It is easy, therefore, to conceive how the inter- 
mittent action of waves, currents, and tides, may 



Ch. II.3 HOUIZONTALITT OF 8TBATA. 35 

sort the sedknent broi^t down from the waste 
of a granitic country, and throw down the mica, 
layer after IsLyer^ separately from the mud or sand. 
Oriffinal harizontaUfy. — It has generally been 
said that the upper and under sur&ces of strata, or 
die planes of stratification, as they are termed, are 
parallel. Although this is not strictly true, they 
make an approach to parallelism, for the same 
reason that sediment is usually deposited at first in 
nearly horizontal layers. The reason of this ar- 
rangement can by no means be attributed to an 
original evenness or horizontality in the bed of the 
sea; for it is ascertained that in those places where 
no matter has been recently deposited, the bottom 
of theocean isofien as uneven as that of thedry land, 
having in like manner its hills, valleys, and ravines. 
Yet if the sea should sink, or the water be removed 
near the mouth of a large river where a delta has 
been forming, we should see extensive plains of 
mud and saild laid dry, which, to the eye, would 
appear perfectly level, although, in reality, they 
would slope gendy from the land towards the sea. 
This tendency in newly>formed*strata to assume 
a horizontal positi<Mi, arises principally from the 
motion of the water, which forces along particles 
of sand or mud at the bottom, and causes them to 
settle in hoUows or depressions, where they are 
less exposed to the force of a current than when 
they are resting on elevated points. The velocity 

c 6 



35 HORIZONTALIIT OF STRATA. {Wutli 

of die currei^ and the tiiotion of die siipttAcial 
Wffveb diminishes from tbe snrfaee ^doWnvmnrdfly 
and is least in those depressions where ihe nmter 
is deepest A good illustration of the prinoipfe 
here alluded to, may be sometimes seen la the 
neighbourhood of a volcano, when a seotaon, whe- 
ther natural or artificial, has laid open to view a 
succession of various^coloured layers of sand and 
ashes, which have fallen in showers upon uneven 
ground. Thus let A, B (Fig. 1.) be two ridges, 
with an intervening valley. These original in- 
equalities of the surface have been gradually 
effaced by beds of sand and ashes cde^ the surface 
at e being quite level. It will be seen that al- 
though the materials of the first layers have accom- 
modated themselves in a great degree to the shape 
of the ground A B, yet each bed is thickest at 

T*«'iu t the bottom. At first 

a great many particles 
would be carried by 
their own gravity down the steep sides of A and 
B, and others would afterwards be blown by the 
wind as they fell off the ridges, and would settle 
in the hollow, which would thus become more and 
more effaced as the strata accumulated from c 
to ۥ This levelling operation may perhaps be 
rendered more clear to the student by supposing 
a number of parallel trenches to be dug in a 
plain of moving sand, like the African desert. 




k;«rliifliy. osae.the wind ^ould. sM^.r^siiMt 40 
93gni>'(i£ theee. trcaidftes lo disafipi^, iui4>4)lf 
sunbceiWoald be as uniform a« b^foc^. Nwib 
water «ia motioii cun exert this levelling pqnirc^ 
«i' sianiiar nrntevials move et»ily than..9ir»M<(Qr 
almost all stones lose in water mor« ihim ,a 
ibird < of the .weight which they have in i^r, , tbf 
^lecific .gm^ity of rocks being in general 9Sh^2^ 
when compered to that of water, whiab is esti'^ 
mated at 1. But the buoyancy of sand Qroiud 
would be still greater in the seaj ^s the densi^.^f 
salt water exceeds that of fresh. . 

Yet, however uniform and horizontal may be the 
surface of new deposits in general, there are still 
many disturbing causes, such as eddies in the water, 
andcurrents moving first in one and then inanotber 
direction, which frequently cause irregularities. 
We may sometimes follow a bed of limestone, 
shale, or sandstone, for a distance of many hun- 
dred yards continuously ; but we generally find at 
length that each individual stratum thins out^ Md 

Fig. 2. , .:> , 




"' ■ •" rrn a 



SeeHonqf strata <if sandstone, grUt and oopglom^ate. 

allows the beds which were previously abav,^ ,and 
below it to meet If the materials are coarse, as 
in grits and conglomerates, the same beds can 



DIAGONAL STRATIFICATION, 



[Ttttl. 



carely be traced many yards withoui; varying in 
size, and often coming to an end abruptly. (See 
Fig. 2.) 

There is also another phenomenon of frequent 
occurrenoe. We find a series of larger strata, each 
of which is composed of a number of minor layers 
fdaced obliquely to the general planes of stratifi- 
cation. To this diagonal arrangement the name 
of '^ fiJse stratification ^ has heea given. Thus in 
the annexed section (Fig. 3.) we see seven or eight 




SecHon qf sand at Sandy HUlt near Biggleswade, Bedfordshire. 
Height twenty feet, (Oreen.>aaad fonnation.) 

large beds of loose sand, yellow and brown, and 
the lines a, &, c, mark some of the principal planes 
of stratification, which are nearly horizontal. But 
the greater part of the subordinate laminae do not 
conform to these planes, but have often a steep 



431.11.3 



AHD its CAlttBBL 



dofe, the inclination being sometimes tovards 
opposite points of die oompass. When the sand b 
loose and incoherent, as in die case liere repna* 
sented, the deviation from parallelism of the 
slanting laminae cannot possibly be accounted 
for by any rearrangement of the particles acquired 
during the consolidation of the rock. In what 
manner then can such irregularities be due to 
original deposition ? We must suppose that at the 
bottom of the sea, as well as in the beds of riYen, 
the motions of waves, currents, and eddies often 
cause mud, sand, and gravel to be thrown down 
in heaps on particular spots, instead of being 
spread out nniformly over a wide area* Sometimes, 
when banks are thus formed, currents may cut 
passages through them, just as a river forms its bed. 
Suppose tlie bank A (Fig. 4.) to be thus &rmed 
with a steep sloping side, and the water being 




c J> 

in a tranquil state, the layer of sediment No. I. 
is thrown down upon it, conforming neaiiy to 
its sur&ce. Afterwards the other layers, 2, d» 4, 
may be deposited in succession, so that the bank 
B C D is formed. If the current then increases 
in velocity, it may cut away the upper portion of 



40 



BlPn«E M ARK« 



[Ftatl. 



diis mass down to the dotted line e (Fig. 4.), and 
deposit the materials thus removed &rther mi, so 
as to form the layers 5, 6, 7, 8. We have now the 
bank B C D E (Fig. 5.), of which the. sur&ce is 

Fig. 5. 




almost level) and on which the nearly hoiizosital 
layers 9, 10, II, may tl»n accumulate* The op^ 
posite slope of ..the diagonal layers of successive 
strata, in the section Fig. 3., may be accounted 
for by changes in the direction of the tides and 
currents in the same place. 

Tlie ripple mark, so common on the surface 
of sandstones of all ages (see Fig. 6.), and which 
is so often seen on the sea-shore at low tide, 
seems to originate in the drifting of materials 
along the bottom of the water, in a manner 
very similar to that which may explain the iiH 
clined layers above described. This ripple is 
not entirely confined to the beach between- bigk 
and. low water coark, but is also produced.* Off 
sands which are constantly covered by yf^f$j^^ 
Similar undulating ridges and furrows iii^.aka be < 
sometimes seen on the surfaoe of (kiftf^qoif aodt. 
blown sand. The followipg is ihe maiipe?' ul- . 
which I once observed the motion of the airr^x^* ' 




produce this effect on a large extent of level 
beacb, exposed at low tide near Calais. Clouds 
of fine white sand were blown fiwm the neigh- 
bouring dunes, so as to cover the shore, and 
whiten a dark level surface of sandy mud, and 
this fresh covering of sand was beautifully 
rippled. On levelling all the small ridges 
and Arrows of this ripple ever an area several 
yards square, I saw them perfectly restored in 
about ten minutes, tlie general direction of the 
ridges being always at right angles to that of the 
wind. The restoraUon began by the appearance 



1^ BtPPUS MaBK. Lt^utl. 

here and there of small detached heaps of sand, 
whleh soon lengthened and joined together, so as 
to iona long sinuous ridges with intervening 
furrows. Each ridge had oneside slightly inclined, 

Fig. 7. 




and the other steep; the lee side being always 
steep, as &, Cj^^d, e; the windward side a gende 
slope, as a, &, — c^ d^ Fig. 7. When a gust of wind 
blew with sufficient force to drive along a cloud of 
sand, all the ridges were seen to be in motion at 
once, each encroaching on the furrow before it, and, 
in the course of a few minutes, filling the place 
which the furrows had occupied. The mode of 
advance was by the continual drifUng of gnuos of 
sand up the slc^>e8 a b and e d, many of which 
grains, when they arrived at b and c4 ^1 over die 
scarps b c and d e, and were under ehdter from 
-die wind; so that they remained 43tationary, 
resEting, according to their shape and momentum, 
an different parts of the descent, and a few only 
rolling to the bottom* In this manner each ridge 
was distincdy seen to move slowly on as often as 
die force of the wind augmented. Occasionally 
part of a ridge^ advancing more rapidly than the^ 
-iMt, OFertook the ridge immediately before it, 
and became eoaofiMinded with it, dms causing dsoee 
bifiireations and branches which are so common, 



ch. 113 ^o^ ji^rmedl 43 

and two of which are seen in the slab Fig. 8. 
We may observe this configuration in sandstones 
of aU ages, and in them also, as now on the sea- 
coast, we may often detect two systems of ripples 
jinterferin^g with each other; one more ancient and 
half effaced, and a newer one, in which the grooves 
and ridges are more distinct, and in a different 
direction* This aro&sing of two sets of ripples 
arises from a change of wind, and the new 
direction in which the waves are thrown on the 
Sihore. 



44 



CHAPTER IIL 

ARRANGEMENT OF FOSSILS IN STRATA — FRESHWATER AND 

MARINE. 

Successive deposition indicated by fossils — Limestones 
formed of corals and shells — Proofs of gradual in- 
crease of strata derived from fossils — Serpula attached 
to spataogus — Wood bored by teredina — Tripoli and 
semi-opal formed of infusoria — Chalk derived principally 
from organic bodies — Distinction of freshwater from 
marine formations — Genera of freshwater and land shells 
— Rules for recognizing marine testacea — Gyrogonite 
and chara — Freshwater fishes — Alternation of marine 
and freshwater deposits — Lym-Fiord. 

Having in the last chapter considered the forms 
of stratification so far as they are determined by 
the arrangement of inorganic matter, we may now 
turn our attention to the manner in which organic 
remains are distributed through stratified deposits. 
We should often be unable to detect any signs of 
stratification or of successive deposition, if par- 
ticular kinds of fossils did not occur here and 
there at certain depths in the mass. At one level, 
for example, bivalve shells of some one or more 
species predominate; at another, some univalve 
shell, and at a third, corals ; while in some form- 
ations we find layers of vegetable matter separat- 
ing strata. 



Cklll.] FOSSILS IN STRATA. 45 

It may appear inconceivable to a beginner how 
mountains, several thousand feet thick, can have 
become filled witli fossils from top to bottom ; but 
the difficulty is removed when he reflects on the 
or^n of stratification, as explained in the last 
chapter, and allows sufficient time for the accu- 
mulation of sediment He must never lose sight 
of the fact that, during the process of deposition, 
each separate layer was once the uppermost, and 
covered immediately by the water in which aquatic 
animals lived. Each stratum, in fact, however 
far it may now lie beneath the siuface, was once 
in the state of loose sand or soft mud at the bot- 
tom of the sea, in which shells and other bodies 
easily became enveloped. 

By attending to the nature of these remains, 
we are often enabled to determine whether the 
deposition was slow or rapid, whether it took place 
in a deep or shallow sea, near the shore or far 
from land, and whether the water was salt, brackish, 
orfresb. Some limestones consist almostexclusively 
of corals, and their position has evidently been 
determined by the manner in which the zoophytes 
grew ;. for if the stratum be horizontal, the round 
spherical head of certain species is uppermost, 
and the point of attachment directed downwards. 
This arrangement is sometimes repeated through- 
out a great succession of strata. From what we 
know of the growth of similar zoophytes in modern 



4$ OBADUAL DEP06IXXON l^P^^h 

s^eft,* ve iofer that, tlie rate of increase was' ex- 
tfemei^ slo^y; and seme of the fossils must have 
floarished fiir ages like forest trees, before they 
attained so large a size. During these ag|e%> the 
water remained clear and transparenty for such 
zoophytes cannot live in turbid water.> 

In like' manner^ when we see thousands of full-- 
grown shells dispersed every where throughout a 
long series of strata, we cannot doubt that time was 
required for the multiplication of successive gene- 
rations ; and the evidence of slow accumulation is 
rendered more striking from the proofs, so often 
discovered, of fossil bodies having lain for a time 
on the floor of the ocean after death, before they 
were imbedded in sediment. Nothing, for ex<- 
ample, is more common thaiH^ to^ see fossil oysiaers 
in clay^ vritb serpulsB, aeorn-shells,, coralsy and 
other creatures, attached to the inside of the valve^ 
so that the mollusk was^ certainly not buried lA 
argillaceous mud the moment it died* There 
must have been an interval during whiish it was 
still surrounded with clear water,, when the tes^ 
tacea^ now adhering to it, grew fVom an embiyo 
state to itill maturity. Attached shells which are 
merely external, like some of the serpula? in tbe 
annexed figure (Fig. 8.),. may* often have grown- 
upon an oyster or other shell while the animal 
within was still living ; but if they are found on 
the inside, it could only happen after the death 



IttMeATXD BY POBflU. 




of the inhabitant of the shell which : 
^ support. ThuBj in Fig. 8., it viU be seen 
Ibit two serpolie have grown on the interior, one 
of tbem exactly on the place where the adductor 
niascle of the Gtyphaa (a kind of oyster) wax 
B»td. 

Some fossil shells, even if simply attached to 
the outside of others, bear full testimony to tlie 
conclusion above alluded to, namely, that an. in- 
terval elapsed between the death of the creature 
to whose shell they adhere, and the burial of the 
Ume in mud or sand. The sea-urchins, or Echini, 
w abundant in white chalk, afford a good illua- 



48 QBADUAL DEPOSITION [Putr. 

tration. It is well known that these animals, wheD 
living.are invariably covered with numeroua spines, 
which serve as organs of motion, and are si^ 
ported by rows of tubercles, which last are only 
seen after the death of the sea-urchin, when the 
spines have dropped off. In Fig. 10. a living spe- 
Fig. 9- Fig- to- 




cies of Spalangus, common on our coast, is repre- 
sented with one half of its shell stripped of the 
spines. In Fig. 9. a fossil of the same genus from 
the white chalk of England shews the naked sur- 
fitce which the individuals of this family exhibit 
when denuded of their bristles. The full-grown 
Serpttla, therefore, which now adheres externally, 
could not have begun to grow till the Spatangus 
had died, and the spines were detached. 

Now the series of events here attested by a sin- 
gle fossil may be carried a step farther. Thus, 
for example, we often meet with a sea-urchin in 
the chalk {see Fig. 11.), which has fixed to it the 
lower valve of a crania, an extinct genus of bivalve 




a. in.] INDICATBD BY nMSILS. 49 

.mDlIa3C&. The^upper valve (6 Fig. 11.) is almort 
" Fig. li. invariably wanting, though oc- 

casionally found in a perfect 
state of preservation in white 
chalk at some distance,- In this 
case, "0 see clearly that the sea- 
^ uicliin first lived from youth to 
' - *" age, tlicn died aitd lost its spines, 
which were carried away. Then 
the yoiiug Crania adhered to the bared shell, and 
perished in its turn ; after which the upper valve 
was separated from the lower before the £chimu 
became enveloped in chalky mud. 

It may be well to mention one more illustration 
of the manner in which single fossils may some- 
times throw light on a former state of things, both 
in the bed of the ocean and on some adjoining land. 
We meet with many fragments of wood bored by 
ship-worms at various depths in the cUy on which 
I^ndon is built. Entire branches and stems of 
trees, several feeb in length, are sometimes dug 
out, drilled all over by the holes of these borers, 
the tubes and shells of the mollosk still remaining 
in the cylindrical hollows. In Fig. 19., e, a 
representation is given of a piece of recent wood 
pierced by the Teredo navalUy or common ship- 
vorrn, which destroys wooden piles and ships'. 
When the cylindrical tube d has been extracted 
from the wood, a shdl is seen at the larger ex- 



:S0 BBADUAI. DEFOaiTIOS [TBI L 

tremlty, composed of two pieces, as shown at e. 
In like manner, a piece (^ fossil wood la, !Flg. 12.) 
has becB perforated l^ an animal of a kindfed 
but extinct genua, called Tertdina hy Lamarck. 
The bakareous tube of this nuJlusk was united 

Fig. 13. 




ifpafiiraiiigm, 
'tig. 1 S. a. Fosnl wood from London els;, bored by Teredina. 

b. Shell end tube of Ten^wi penonata, tbe right band 
figure llie Tentnl, Ibe kn tfae dorul view. 
Fig, is. I. Recent wood bored bj Tertdo. 

d. Shell end tube of Tereda nataSt, from the ume. 
Aatenor and poMenor Tiew at ttie tiItc* of mnc 
detached from the tube. 

and as it were soldered on to the valves of the 
shell ifi), which therefwe cannot be detached from 
the tube, like the valv^ of the recent Teredo. 
The wood in this fossil specimen is now con- 
verted into a stony maas, a mixture of clay 
and lime ; but it must once hare been buoyant 
and floating in the sea, when the Teredinse 



Cb.ni} IKPICAXED BY JOSSILa 5| 

lived upon itf perforating it in ail directions. 
Again^ before the infant colony settled upon tlie 
drift wood, the branch of a tree mu»t have. been 
floated down to the sea by a river, uprooted^ 
perhaps, by a flood^ jot tora off and cast into the 
waves by wind; and thus. our thoughts are car- 
• ried back to a prior period, when the tree grew 
for years on dry land, enjoying a fit soil and 
climate. 

It has been already remarked that there are 
rocks ih the interior of continents, at various 
depths in the earth, and at great heights above 
the sea, almost entirely made up of the remains of 
z<^phytes and testaeea. . Such masses may be 
compared to modern oyster-beds and coral reefs ; 
and, like them, the rate of increase must have 
been extreniely gradual* But there are a variety 
of stony deposits in the earth's crust now proved 
to have been derived from plants and animals of 
which the organic origin was not suspected until of 
late years, even by naturalists. Great surprise 
was therefore created by the recent discovery of 
Professor Ehrenberg of Berlin, that a certain 
kind of siliceous stone, called tripoli, was entirely 
composed of millions of the skeletons or cases of 
microscopic animalcules. The substance alluded tb 
Imi Ikmg been well known in the arts, being used 
in the fiatm. cxf |>owder for polishing stones and 
metals*' ' It faas'beeh procured, among other places, 

D 2 



52 INFUSORIA IN TRIPOLI.: IParH 

froni Bilin, in Bohemia, where a single stratum^- 
extending over a wide area, is no less than 14 feet 
thick. This stone, when examined with a power- 
ful microscope, is found to consist of the siliceous 
cases of infusoria, united together without any 

Fig. 14. Fig. 15. Fig.'16. 




mMm 




Bacillarifi GaiUanetta GaUUmeOa 

vu^eruf dbtatu. femif>jmea% ^ 

These figures are Tnagnified nearly 300 times, eaecept the AnneK 
figure of G. ferruginea {Fig. \6,a),whichismag9iyied2QOOtimes» 

Visible cement. It is difficult to convey an idea 
of thdir extreme minuteness ; but Ehrenberg esn 
timates that in the Bilin tripoli there are 41,000 
millions of individuals of the GaUhneUa distant 
(see Fig. 15.) in every cubic inch, which weighs 
about 220 grains, or about 187 millions in a single 
grain. At every stroke, therefore, that we make 
with this polishing powder, several millions, per-^ 
haps tens of millions, of perfect fossils are crashed 
to atoms* 

The shells or. shields of these infusoria are of 
pure silex, and their forms are various, but very 
inarked and constant in particular genera and 
species* Thus, in the family Bacillaria (see 
Fig« 14.), the fossil species preserved in tripoli are 
Been to exhibit the same divisions and transverse 
^ines which characterize the living shells of kindred 



ClLtU3 INPOaOBTA IK TRIPOLI. 53 

(brio. With these, also, the siliceous spicule or 
internal supports of the freshwater epoage, or 
^ongiUa of Lamarck, are sometimes intermingled 
(see the needle-shaped bodies in Fig. 16.). These 
fliaty cases and spiculse, although bard, are very 
fragile, breaking like glass, and are therefore ad- 
mirably adapted, when rubbed, for wearing down 
into a fine powder fit for polishing the surface of 
metals. ' 




^e- IT. Nalnnl are. 

^'p IS. The lame magnified, showing dicular siticuUtiona of > 
■pecie* o( GadloneBo, and spiculm of ^onffiUt. 

3 



54 ' F08SIL INFD80BIA. . FPtett 

Besides the tripoli, whicli is formed exclusiirely 
of infusoria, there occurs in the Trpper part of the 
l^eat stratum at Bilin another heavier and more 
compact stone, a kind of semi-opal, in which in*- 
nttmerable parts of infusori!! and spicnls of the 
Spongilla are filled with, and cemented together 
by, siliceous matter. It is supposed that the shells 
of the more delicate animalcules have been dis* 
solved by water, and have thus given rise to this 
opal, in which the more durable fossils are pre- 
served like insects in amber. This opinion is 
confirmed by the fact that the «nall shells de- 
crease in number and sharpness of outline in pro- 
portion as the opaline cement increases in quantity. 

In the Bohemian tripoli above described, as in 
that of Planitz in Saxony, the species of infusoria 
are freshwater ; but in othep countries, as in the 
tripoli of the Isle of France, they are of marine 
species, and they all belong to formations of the 
tertiary period, which will be spoken of hereafter. 
(See Part II.) 

A well-known substance^ called bog-iron ore, 
often met with in peat-mosses, has also been shown 
by Ehrenberg to consist of innumerable articu- 
lated threads, of a yellow ochre colour, composed 
partly of flint and partly of oxide of iron. These 
threads are the cases of a minute animalcule^ 
called GaiUoneUa ferruginea (Fig. 16.). 

It is dear that much time must have been 



Cl.III.3 MICROSCOPIC FOS8IL9. 5|^ 

qoired lor the accuniiilation of strata fo which 
countless generations' of infusoria have contributed 
their shells ; and these discoveries lead us natu* 
lally to suspect that other deposits, of which the 
materials have usually been supposed to be 
inorganic, may in reality have been derived from 
microscopic organic bodies. That this is the case 
with the white chalk, has often been imagihedy 
this rock having been observed to abound in a 
variety of niarine fossils, such as shells, echini^ 
corals, spoi^es, tDrttstac6a,.and fLAibs; 'Mr. Lons* 
dale^ oh examining lately, in the nausepm of the 
Geological Society of London, pdrtionfi of white 
chalk from different parts' of England, found, on 
carefully pulverizing them in water, that what 
appear to the eye simply as white grains were, in 
fact, well-preserved fossils. He obtained about a 
thousand of these from each pound weight of ehalk, 
some being fragments of minute' corallines, others 
entire Foraminifera and Cy therinse. The annexed 
drawings will give an idea of the beautiful forms 

CytheriiUB and Foramin^era from the cbaik* 
Fig. 1 9. Fig. 20. Fig. 91. Fig. 22. 



M H '^ "^ 



C^itkerimt. Portion qf Lentictdinay JMOi. DUcorbfs. 

Nodo$aria. {Operculma, D*Orbi) 

of many of these bodies. The figures a a repre- 
sent their natural size, but, minute as they seem, 

D 4 



^' INVUSOKIA IN FLnrrS^- tl^artl,, 

!)ie sitiafiest of them, such as a, l^ig. ^4 ai*^ 
j^g^ntic in comparison with the cases of infusoria 
before mentioned. There is, moreover, good reasoii 
to beKeve that the chambers into which th^se 
Foraminifera are divide are actually Cftetx filled. 
with hundreds of infusoria; for many of the minute 
grains which they contain, and which compose the 
enveloping chalk, have been observed, uride;- a 
powerful microscope, to consist of circular discs, 
like the articulations of Gailbnettd, before repre^ 
sented in Fig. 18. The bodies alluded to were, 
calcareous ; but Ehrenberg hasr discovered oth^i^ 
in the flints of the chalk, which, like thd infusoria 
in tripoli, are siliceous. These forms are especially 
apparent in (iie white coating of flints, often ac- 
companied by innumerable needle-shaped spicules 
of sponges : and the same are occasionally visible 
in the central parts of chalk flints where they, 
are of a lighter colour. After reflecting on these 
discoveries, we are naturally led on to conjecture 
that, as the formless cement in the semi-opal of 
Bilin has been derived from the decomposition of 
animal remains, so also even those parts of chalk 
flints in which no organic structure can be recog- 
nized may nevertheless have constituted a part of 
microscopic animalcules, 

** The dust we tread uppn was once alive I " ^^JByron, 

How faint an idea does this exclamation of the 



eii. 1113 9LOW I>J5X»OS1TION Qfr SI:raTA. Jjff 

poet c^yeyof the re^ Woii()i&r9 of nature! Suf 
her^ y^ discover proo^ that the calpareou^ aod 
siliceous dust of which hills are oompo^ ha9 nQ% 
only, been once alive, but almost every part|cl^ 
llbeit invisible to the naked eye, ^till reUdn^ H^ 
organic structure which, at periods oC dme iacat» 
culably remotes wa« impressed upou it by th^ 
powers of life, ... 

As I have dwelt upon the proo&of theglown«s» 
with which fossUiferous strata in general have bees^ 
produced, I may remark that some writers hav^ 
ar^ued^ from the appearances of certain deposits 
containing coal, that sedimentary rocks of great 
thickness have been accumulated with rapidity^ 
This conclusion has been drawn chiefly from a 
remarkable phenomenon, — the position of the 
trunks of fossil trees intersecting obliquely, and 
often at right angles, the planes of nmny strata^ 
For a full examination of this question, the reader 
is referred to the chapter on the carbmiferou| 
formations, in the sequel ; and I shall merely ss^ 
here, that, although partial deposits have hoel^ 
thrown down in the spots where thes^ foi^sil tree^ 
occur in a comparatively short lapse of time, yet 
we can by no means infer that a similar rat» f>f 
increase of carboniferous rocks prevaileji slmylta^ 
neously over a wide area. On the othqr hand, the^ 
vegetable origin of coal is now universally ad-? 
naitted by geologists ; and, when we di^viss.t^h^ 

P 5 



*S8 DltHNCnOK 01^ nttiSHWATER iVuit, 

probable manner in wliich the terre$trtel plains 
from which it was derived were imbedded in 
marine shale and sandstone, we shall find it neces* 
sary to suppose a long succession of opetations. 

Freshwater and marmefossih,---' StrsitSLy whether 
deposited in salt or fresh water, hare the sam^ 
forms; but the fossils are very different in the two 
cases, for the same reason that aquatic animals 
which frequent lakes and rivers are distinct from 
those inhabiting the sea. As an example of 
English strata characterized by freshwater fossils, 
I may point out a formation, which extend over 
the northern part of the Isle of Wight, composed 
of marl and limestone more than fifty feet thick. 
The shells are principally, if not all, of extinct 
species ; but they are of the same genera as tliose 
now abounding in ponds and lakes, either in our 
own country or warmer latitudes. 

In many parts of France, as in Auvergne, for 
example, strata of limestone, marl, and sandstone 
occur, hundreds of feet thick, which contain ex- 
clusively freshwater and land shells, together with 
the remains of terrestrial quadrupeds. The num- 
ber of land shells scattered through some of these 
freshwater deposits is exceedingly great; and there 
are even districts where the rocks scarcely contain 
kny other fossils except snail-^shells {helices) ; as, for 
instance, the limestone on the feft bank of the 
Rhine, between Mayence and Worms, at Oppen- 



Cb. ini • FBOM MASniK FOSIUTlOHa in 

heim, Findheini) Budenheim, and other placets 
In order to account for this phenomenon, tbt 
geologist has only to examine the small deltas of 
torrents which enter the Swiss lakes when the 
waters are low, such as the newly«formed plain 
where the Kander enters the Lake of Than. He 
there sees sand and mud sti*ewed over with inno* 
merable dead land shells, which have been brought 
down from valleys in the Alps in the preceding 
spring, during the melting of the snows. Again, 
if we search the sands on the borders of the Rhine, 
in the lower part of its course, we find countless 
land sheils mixed with others of species belonging 
to lakes, stagnant pools, and marshes. These 
individuals have been wa^ed away firom the 
alluvial plains of the great river and its tributaries, 
some from mountainous regions, others from the 
low country. 

Although freshwater formations .are often of 
great thickness, yet they aPd usually very limited 
in area when compared, to marine deposits, just 
as lakes and estuaries are of small dimensions in 
comparison with seas* 

We may distinguish a freshwater formation, 
first, by the absence of many fossils almost invari- 
ably met with in marine strata. For example, 
there are no corals, no sea-urchinsy and scarcely 
any other zoophytes ; no chambered shells^ such 
as the nautilus, nor microscropic Foraminifera. 

D 6 



QQ. I>I8TlNCnOK OF WaSSaWAXEB, X^mfU 

But it is chiefly by attending to the forms of thd 
molliiaea-^iat we are guided in det^mining the 
point in question. In a freshwater deposil^ the 
niimber of incfividual shells is often as greats if 
no^ greater, than ia a marine stratum ; but there 
are fewer species and genera. This might be 
anticipated from the fact that the genera and 
species of recent freshwater and land shells are 
few when contrasted with the marine. Thus, the 
genera of true mollusca according to Blainville's 
system, excluding those of extinct species and 
those without shells, amount to about 200 in 
number, of which the terrestrial and freshwater 
genera scarcely form more than a sixth. * 

Almost all bivalve shells, or those of acepha«> 
}ou§ mollusca, are marine, about ten only out of 
ninety genera being freshwater. Among these 
last, the four most common forms, both recent and 
fossil, are Cyclas, Cyrena, Unio, and Anodonta 
j(see figures) ; the two first and two last of which 
are so nearly allied as to pass into each other« 

Fig. 23. Fig. 24. 




Qfelai9bo9atai twul, Haoti. CyreiM tr^^qmtia s fouSl Grays, Eiiex. 

# See Synoptic Table in Blainville's Malacologie. 







Lamarck divided the bivalve moUusca into the 
Dimyajy, or those having two large muscular im- 
pressions in each valve, as a i in the C;rc]as, Fig. 23. , 
and the Monomyary, such as 
the oyster and scallop, in 
which there is only one of 
these impressions, as ia seeo 
in Fig. 28. Now, as none of 
these last, or the unimuscular 
bivalves, are freshwater, we 
may at once presume a de- 
posit in .which we find any of them to be 
marine. 

TTie univalve shells most characteristic of fi-esht 
water deposits are, Planorbis, Limnea, and Palu- 
dina. (See figures.) But to these are occasionally 
added Physa, Succinea, Ancylus, Valvata, Mela- 
nopsls, Meiania, and Neritina. (See figures.) 





In regard to one of these, the Ancylus (Fig. 
33.), Mr. Gray observes that it sometimes difTers 
in 'no respect from the marine Siphonaria, except 
in the animal. The shell, however, of the An- 
cylus ia usually thinner. • 

• Gray, Hiil. Traos., 1835. p. SOS. 



C)t.in.l nfOX MAKING FORMATIOim. S3 

Some naturalists include Neritina (Fig. 40.) 
and the marine Nerita (Fig. 41.) in the same 
genus, it being scarcely possible to distinguish the 
two by good generic characters. But, as a general 
rule, the fluviatile species are smaller, smoother, 

Fig. 40. Fig. 41. 




NerMna globului, Pari< basin. Nerita granulota. Paris buln. 

and more globular than the marine; and tliey 
have never, like the Neritae, the inner margin of 
Fig. 42. the outer lip toothed or crenulated. (See 
Fig. 41.) 

A few genera, among which Cerithium 
(Fig. 42.) is the most abundant, are com- 
mon both to rivers and the sea, having 
i^ecies peculiar to each. Other genera, 
like Auricula (Fig. 36.), are amphibious, 
living both in freshwater and on land. 

The terrestrial shells are all univalves. 
The most abundant genera among these^ 
ceriohtm both in a recent and fossil state, are 
Paris basin, Efelix (Fig. 45.), Cyclostoma, Pupa, 
(Fig. 44v), Clausilia, Bulimus (Fig. 43.)5 and 
Achatina'; whicTi. two last are nearly allied and 
pass iiito each other. The sanie may be said 
with almost equal truth of Pupa and Clausilia. 




04 DmiNCTlDH OF FRESHWAi'ER 

Fig. 13. Fig. 44. Fig. 45. 



4 e @ 




Satiima rupa mun.-grHK. BrOi pleUiiim. 

yiU Ttvcni : aid dUofiitBljTom Loot of Biine. 

The Ampullaria (Fig. 46.) is another genus of 

Fig. 46, sbells, inhabiting rivers and ponds 

in hot countries. Many fossil 

species have been referred to this 

genus, but they have been found 

chiefly in marine formations, and 

are suspected by some concho- 

"fr^Tft^^^^ legists to belong to Natica and 

other marine genera. 

. All univalve shells of land and fi%gh water 
species have entire mouths ; and this circumstance 
jnay often serve as a conveniem rule for dbtin- 
gubhing freshwater from marine strata j since, if 
any univalves occur of which the mouths are not 
^tire, we may conclude that the formation is 
piarine. The aperture is said to be entire in such 
shells as the Ampullaria and the land shells 
%ured in this page, when its outline is not inter- 
rupted by an indentation or notch such as that in 
Ancillaria (Fig. 48.) j or is not prolonged into a 
f^nal, as that seen at a in Pleuromota (F^g. 47.). 
The mouths of a large proportion of the marine 
univalves have either these notches or canals, and 



C^liq fBOM MARIME FORMATIONS. ' 



Fig. At- 




ndalita, LoMkm ilar- 



allthesespecies are, without exception, camirorcHis; 
whereas nearly all testacea having entire mouths, 
are plant-eaters, whether the species be marine, 
freshwater, or terrestrial. 

There is, however, one genus which alTords an 
occasional exception to one of the above rules. The 
Ceritbium {Fig. 42.), although provided with a 
short canal, comprises some species which inhabit 
salt, others brackisb, and others fresh water. 

Among the fossils very common in freshwater 
deposits, are the shells of Cypris, a nii^ute crus- 
taceous animal, having a shell much resembling 
that of the bivalve mollusca.* Many minute 
living species of this genus swarm in lakes and 
stagnant pools in Great Britain; but their sheQs 
are not, if considered separately, conclusive as to 
the freshwater origin of a deposit, because an-' 

« See figures in chap, on Wealden, Port II> 



ea 



DUnKGTIOK OF FEXSHWATnt 



C^Wtt 



Other kindred genus of the same order, the Cythe- 
rina of Lamarck (see Fig. 19« p. 55.), inhabits salt 
water ; and, although the animal differs slightly^ 
the shell is undistinguishable from that of the 
Cypris. 

The seed-vesdels of Chara, a genus of aquatic 
plants, are very frequent in freshwater strata. 
These seed-vessels were called, before their true 
nature was known, gyrogonites, and were supposed 
to be shells. (See Fig. 49. a.) 

Fig. 49. Pig. 50. , 




Chora medieaghada : 
fossil. Isle of Wight. 
Oy Sced-vettel, 

magnified 20 

diameters. 
h^ Sten^ magnified. 



Ckara elattiea / receni, Italy. 
Of Sessile seed-vessel between the diviuiMi- 

of the leaves of the female plant. 
hy Transverse section of a branch, with five 

seed-vessels magnified, seen from below 

Bpwards. 

The Charffi inhabit the bottom ,of lakes and 
pon.d% and flourish mostly where the water is 
charged with c^^r^onate of lim^. Their seed- 
vessels are covered with a very tough integument^ 
capable of resisting decomposition ; to which cir- 
cumstance we may attribute their abundance in a 
fossil state. The annexed -figure (Fig. 50.) repre- 



eb. I»^] 9BOM XAftlNB FOBJf ATIOKa 67 

Eetits a branch of one of many new species found 
}ij Professor Amici in the I^kes of northern Italjr* 
The s^d-vessel in this plant is more globular than 
in the British Charse, and therefore more nearly 
resembles in form the extinct fossil species found 
in England^ France^ and other countries. The 
stems, as well as the seed-vessels^ of these plants 
are foupd both in modej-n shell marl and in an- 
cient fre^xwatis^p fqrntations> They are generally 
composed of a large lube surrounded by smaller 
tubes ; the whole stem being divided at certain 
intervals by transverse partitions or joints. (See b^ 
Kg, 49.) 

It is not uncommoii to meet with layers of vege^ 
table matter, impressions of leaves, and branches 
of trees, iij 9trat^ containing freshwater shells | 
and we also fitHl odcasionaily the teeth and bones 
of land quadrupeds^ of species now unknown. 
The manner by which such remains are occasion^ 
ally carried by rivers into lakes, especially during 
floods, has been fully treated of in the ^^ Principles 
of Geology."* 

The remains of fish are occasionally useful in 
determining the freshwater origin of strata. Cer- 
tain genera, such as carp, perch, pike, and loach, 
{Cyprirme^ Perea^ Esoxy and Ccbiiis)^ as also 
LebiaSf being peculiar to freshwater. Other ge^ 

* See Index. " Eossilization/' 



f;$ ALTERNATIONS OF HARINtf it^artt 

hera' contain some freshwater and some marine 
species, as CoUusy MugiU and AnguMoj or eeL 
The rest are either common to rivers and the isea, 
as the salmon ; or are exclusively characteristic of 
salt water. The above observations respecting fos- 
sil fishes are applicable only to the more modern 
or tertiary deposits ; for in the more ancient rock^ 
the forms depart so widely from those of existing 
fishes, that it is very difficult, at least in the pre^ 
sent state of science, to derive any informatioii 
from icthyolites, respecting the element in which 
f trata were deposited. 

The alternation of marine and freshwater form- 
ations both on a small and large scale, are facts 
well ascertained in geology. When it occurs oii 
a small scale, it may have arisen from the alternate 
occupation of certain spaces by river-water and 
the sea ; for in the flood season the river forced 
back the ocean and freshens it over a large areas 
depositing at the same time its sediment; after 
vbich the salt water again returns, and, on re* 
sunwg its former place, brings with it sand, mud, 
and marine shells. 

. There are also lagoons at the mouths of many 
fivers, as ^e Nile and Mtssissi{^i, which are di- 
vided off by bars of sand from the sea, and which 
are filled with salt and fresh water by turns« They 
often communicate exclusively with the river for 
months, years, or even centuries ; and then a 



Ch-Ill] AND FRSdHWA'^ FOfiMATlON& g9 

bareach b^ng made in the bar of sand, they are 
for long periods filled with salt water. 

The Lym^Fiord in Jutland offers an excellent 
illustration of ai^alogous changes ; for, in the 
course of the last thousand years, the western ex- 
tremity of this long frith, which is 120 miles in 
length, including its windings, has been four 
times fresh and four times salt, a bar of sand 
between it and the ocean having been as often 
formed and removed. ITie last irruption of salt 
water happened in 1824, when the North Sea 
entered, killing all the freshwater shells, fish, and 
plants ; and from that time to the present, the 
sea-weed Fucus vesiculosus, together with oysters 
and other marine moUusca, have succeeded the 
Cyclas, Limnea, Paludina, and Charae. * 

But changes like these in the Lym-Fiord, and 
those before-mentioned as occurring at the mouths 
of great rivers, will only account for some cases 
p{ marine deposits resting on freshwater strata. 
When we find, as in the south-east of England,' 
a great aeries of freshwater beds, resting upon 
one marine formation of great thickness, and 
again covered by another more than 1000 feet 
thick, we sliall find it necessary t6 seek for a dif^ 
ferent explanation of the phenomena, f 

# See Principles, Indpx, ** Lym-Ficord.'* 
•j* See account of Wealden, Part XL 



70 



CHAPTER IV. 

CONSOLIDATION OF STRATA AND PETRIFACTION OF 

FOSSILS. 

Chemical and mechanical deposits — Cementing together of 
particles — Hardening by exposure to air — Concretionary 
nodules — Consolidating effects of pressure — Minerali^ 
sation of organic remains — Impressions and casts how 
formed — Fossil wood — Goppert's experiments — Pre- 
jcipitation of stony matter most rapid where putrefaction 
is going on — Source of lime in solution — Silex de* 
rived from decomposition of felspar — Proofs of the 
lapidification of some fossils soon after biu'ial, of others 
when much decayed. 

Having spoken in the preceding chapters of the 
forms of stratification, both as dependent on the 
deposition of inorganic matter and the distribution 
of fossils, I may next treat of the consolidation of 
stratified rocks, and the petrifaction of imbedded 
organic remains. 

Chemical and mechanical deposits, — A distinct 
tion has been made by geologists between deposits 
of a chemical, and those of a mechanical, origin* 
By the latter name are designated 'beds of mud^ 
sand, or pebbles produced by the action of nuw 
ning water, also accumulations of stones and 
scoriae thi*own out by a volcano, which have fallen 
into their present place by the force of gravitation. 



fni.iv.3 .coNsoi^mATioN or stbata. 71 

But the matt^ which forms a chemical deposit 
has not been mechanically suspended in water, but 
In a state of solution until separated by chemical 
action. In this manner carbonate of lime is oft^i 
thrown to the bottom of lakes and seas in a solid 
form, as may be well seen in many parts of Italy^ 
where mineral springs abound, and where the 
calcareous stone, called ti^vertin, is deposited. In 
these springs the lime is usually held in solution 
by. an excess of carbonic acid, or by heat if it 
be a hot spring, until the water, on issuing from 
the earth, cools or loses part of its acid. The cal- 
careous matter then falls down in a solid state, 
encrusting shells, fragments of wood and leaves^ 
and binding them together.* 

In coral reefe, large masses of limestone are 
formed by the stony skeletons of zoophytes; and 
these, together with shells, become cemented to- 
gether by carbonate of lime, part of which is pro- 
bably furnished to the sea-water by the decom- 
position of dead corals. Even shells of which the 
animals are still living, on these reefs, are very 
commonly found to be encrusted over with a hard 
coating of limestone, f 

If sand and pebbles are carried by a river into 
the sea, and these are bound together Immediately 
by carbonate of lime, the deposit may be described 

* See Principles, Index, ** Calcareous Springs," &c. 
+ Il)kl. « TVavertin," « Goral reefs," &c. 



39 .Q O f smu mmmi^i^mmmmm. t^^ht 

i.,3i^V»'tlie Ye|iiaric9-drefafy mad^'iiktSflipe^lf; 
Off, th«t QfigpnfliuirizontsUty of smta are' sciridjf 
■«WAwbte Id siediMiical . depo^ta^ and otf 1^ pM^~ 
tiaUy to Xham of a mixed: nature, ' Sudbtasw^ 
p^rely chemi^l may be formed on a-Tfery swep' 
^$)|p%,ar n^j.even oAcmst theivertaeai walk dff ia 
^tu:e^^ apdi lorn of equal tbtcknn» throughout ^ 
^n%. such d^osits .ftre of soiatl ext^H, and M* 
t^e most part eonfin^ to.vein^stones. 

> C(^zn^2;^i ofptirMes^ — < It is chiefly in the (»i6e 
of«calcar^u^ rock9 that solidification takes* plabe 
at t^ ti^0 of deposition. But there are matiy 
deposits, in which a cen^enting process conies into 
operation. Jong, subsequently. We may sometimes * 
p)|B^rve| where the water of ferruginous or cat* 
c^i;epu& .springs has flowed through a bed of sand 
or^rjavi^l, ^X iron or carbonate of lime has been 
d^po^^^ed in the interstices between the gmins or 
p^|)ble§9 ^Q that in certain places the whole has 
be.e|L,boujid together into a sto^e, the same set of 
strata rernaining in other parts loose and incoh«?eftt* 
Proofs of a similar cementing aetion are seen 
in a rock at'Kelloway in Wiltshire^ A pecidiar 
band of sandy strata, belonging to the group called 
Oolite by geologists, may be traced through several 
counties, the sand being for the most part loose 
and unconsolidated, but becoming stony iiear 



ftnJI riidk which have decompoBed, Imfing t&t 
^ iM«t{MM left only tiieir casts. Hie esleib^aras 
matlfer hence deriired has evidetilfy served, at 
iXMBe finwer period, a» a cement t6 the sfiiceoiifl 
gcacna of sand, and thiss a solid sandstone has 
been- prodficed. If vre take fragments of many 
other argBIaceous grits, retaining the casts of 
flheOs, and plnnge them into dilute rtiuriadc or 
other acid, we see them immediately changed into 
common sand and mud; the cement of lime, derived 
from the shells, having been dissolved by the acid. 

Traces of impressions and casts are often ex* 
tremely fiunt. In some loose sands of recent date 
we meet irith shells in so advanced a stage of 
decomposition as to cramble into powder when 
touched. It is clear that water percolating such 
strata may soon remove the calcareous matter of 
die shell ; and, uidess circumstances cause the car- 
hansLte of lime to be again deposited; the grains 6f 
sand will not be cemented together; in which 
case no memorial of the fossil will remain. The 
absence of organic remains from many aqueous 
Todts may be thus explained. 

In some conglomerates, like the puddingstone 
of Hertfordshire, flinty pebbles' and sand are 
united by a siliceous cement so firmly, that if a 
block be fractured the rent passes as readily 
through the pebbles as through the cement. 

£ 



. It is probable that mwy 4trata» l)ecaiD# 9oUi a| 
the time vheu th^ emei^ged firom the waters, iq 
which th^y were deposited) and wh^n they fifi9t 
fenned a pfl^ of the dry Jand. A well-kopwii 
£ict seems to confirm this idea ; by £blv the grealeF 
number of the stones, used for building and road* 
making are much sofider when first taken from tb^ 
quarry than after they have beea long: e^^posed tQ 
the auv Hence it is found d^siraUe to. shape tb^ 
stones which are to be used in architecture whil^ 
they are yet soft and wet, and while they contajn 
theijr ^^ quarry-water," as it is called ; also to break 
up stone intended for roads when soft, and then 
leave it to dry in the air for months that it ma^ 
harden* Such induration may perhaps be aer 
counted for by scq>posing the water, which pene? 
trates the minutest pores of rooks^ to deposit chi 
evaporation carbonate of lime^ iron, sikoc* and 
other minerals previoudy held in scdution, Thes^ 
particles, on crystallising^ would not only be de- 
prived themselves of freedom of motion, but would 
also bind together other portions of the rock which 
before were loosely aggregated. On the same 
principle wet sand and mud become as hard as 
stone when frozen ; because one ingredient of the 
mass, namely, the water, has crystallized, so as 
to hold firmly together all the separate . particles 
of which the loose mud and sand were composed. 
Dr. MacCuUoch mentions a sandstone in Sky, 



|ni.nrj €0K80I.IDATf(m op gXRATi^. 9A 

ivych may te moulded like doogh when first 
found; and another fmm China, which is <!ompress« 
iUe by the hand when immersed in wMer» But 
it is not mc^ly these compounds wUch readily 
admit water to penetrate into them ; some simple 
mineFalss says the same writer,- which afe rigid 
and as hard as glass in our cabinets^ are ofteq 
flexible and soft in their native beds ; this is th^ 
esse with asbestos, sahlite, tremolite, andcalcedony, 
and it is reported also to happen in the case of 
the beryL* 

The marl recently deposited at the bottom of 
Lake Superior, in North America, Is soft, and often 
^led with fresh-water shells; hot if a piece be taken 
np and dried, it becomes so hard that it can only 
be broken by a smart blow of the hammer. If the 
kike therefore was drained, such a deposit wonld 
be found to consist of strata of marlstone, like that 
observed in many ancient European formfations, 
and like ihem containing fresh-water l^bd[]^.f 

It is probable that some of the heterogeneous 
material which rivers transport to the sea may 
at once set nnder water, like the artificial mixture 
called pozzolana, which consists of fine volcanic 
sand charged with about 20 per cent, of iron, and 
the addition of a small quantity of lime. This 
substance hardens and becomes a solid stone in 

♦ Dr. MacCuUoch, Syst. of Geol. vol.i. p. 123. 
t Prini. of Geol., Index, " Superior, Lake." 

£ 2 



water; and was used by the Romahs'M constrtifetliig 
the foundations of buildings lA the sea. =' ''^' 

' 'Congblid&tion in these cases is broiight about 
by the action of chemical affinity on fiiiely bbrhihi^ 
huted matter previously suspended in water.' After 
deposition similar particles seem to exert t mutual 
attraction on each other, and congregate togiethei* 
in particular spots, forming lumps, nodul^ and 
concretions. Thus in many argillaceous deposits 
there are calcareous balls, or spherical concretions, 
ranged in layers parallel to the general stratifica'> 
tion ; an arrangement which took place after the 
shale or marl had been thrown down in successive 
laminae ; for these laminae are often traced in the 
concretions, remaining parallel to those of thesur- 
Fig. 51. rounding uhconsoli* 

dated rock. (SeeRg. 
61.) Such nodules 
of limestone have 



••1-* 



caicareout nodtott in Lias. often a shell or Other 

foreign body in the centre. * 

Among the most remarkable examples of concre- 
tionary structure are those described by Professor 
Sedgwick as abounding in the magnesian lime- 
stone of the north of England. The spherical balls 
iare of various sizes, from that of a pea to a diameter 
of several feet, and they have both a concentric and 

* See De la Bechc's Geological Research^, p. 95. 



jZ 



J I «■ 



!-*: 



• ? : ^g^= = fcv" 







2^^ 



CMV.3 :,.j^ ,9fs^TmfXi 9ftCKa>^ . JJ7 

;94isM^,^^i^Uirf&^,ii«4»ile at. the same time the 
laminde of opgimd. deyposition piifl9 unmt^rrtijptedly 
t|^i$(^^<theu;u .Iq sotne.clifia this limestone ^e« 
s^ll^es a.gveat yr^^^ar pile of cannon balls, 
§0196 of ijbe. globular inasses have their centre in 
qw :^tx^tijan, while. ^. portion of their exterior 
pflfses .thrpugh tp the stratum above or below. 
T!ims, ijke l^ger spheroid in the anni^s^ed section 
t . ^. 5& (Fig. 52.) pass^ from 

J the stratum b upwards 
into (T* In this instance 
we must, suppose the 
deposition of a series 

spheroidal toncr^fiom tnnuignttian * ^ 

umesione. of minor layers, first 

forming the stratum .2s and afterwards the in- 
piimbept stmtum a^ then a moveipent of the 
particles to^ok place, and the carbmiates of lime} 
and magnesia separated from the more impureand 
mi^fied ni4tt^r forming the still unconsolidated 
parts of the. stratum* Crystallization? beginning 
at the centre, must haye gone on fo:j:niing coi^- 
Mnitrie eoats, around the original nucleus without 
interfering witji the laminated stru<*jure^pf the 
rock. As to the radiations from, a centre it is, a 
phenomeaon wbiph, hQwevear sii^ujar, is common 
in spherical concretions of varioMS mineral ingred- 
ients. ... 

When the particles of. rocks have been thus 
re-anwige4.]b)y. chemical forces, it is sometime^ 

E,3 




f^ comouftATidir or itbAta c^Mti^ 

diiicrit or in^ssdile (oascettaibi <«iiietiieF eertftiti 

lines of diTision are due to originid depottdon or 

to the subsequent aggregatSoa of siiHiiaT {Murtades* 

Flf. 43, Ihm suppose three 

f strata of grit^ A^ B^ C9 
&fe charged unequally 
with calcareous matter, 
and that B is the most calcareous. If consoltda* 
tion takes place in B, the concretionary action may 
spread upwards into a part of A, where the car- 
bonate of lime is more abundant than in the 
rest; so that a mass, dy.effi j&irmmg a portion of 
the superior stratum, becomes united with B into 
one solid mass of stone. The original line of 
dirision, d, e^ being thus eflaeed, the line, d, fi 
Would generally be considered as the sur&ce of 
the bed B, though not strictly a true plane of 
stratification. 

Presstire and heat. — When sand and mud sink to 
the bottom of a deep sea the particles are not 
pressed down by the enormous weight of the in<^ 
cumbent ocean; for the water, which becomes 
mingled with the sand and mud, resists pressure 
with a force equal to that of the column of 4uid 
above. The same happens in r^ard to organic 
remains which are filled with water under great 
pressure as they sink, otherwise they would be 
immediately crushed to pieces and flattened. 
Nevertheless, if the materials o^ a atratom ivinaiii 



ID a yidding stal^ (aid 4o &et filec or solidify, tft«]r 
Will be gradiiftlly fMpieeaed down by the weight of 
other matermb snceessiTdy heftped upon themy just 
la soft clay or loose satid on whidi a hoiiae is built 
may give way. ^ such downWaird pressure par« 
Mcks of clay» sand> and marl may become packed 
into a smaller space^ and be made to cohere 
together perman^itly. 

Analogous effects of condensation may arise 
wh^i the solid parts of the earth^s crust are forced 
in various directions by those mechanical move* 
meats afterwards to be described^ by which strata 
have been bent, broken, and raised above the level 
of the sea* Rocks of more yielding materials must 
often have been forced against others previously 
consolidated, and, thus compressed, may have 
acquired a new structure. 

But the action of heat at various depths in the 
earth is probably the most powerful of all causes 
in hardening sedimentary strata. To this subject 
I shall refer again when treating of the meta« 
morphic rocks, and of the slaty and jointed 
structure. 

Mineralization of organic rewimw*.— The changes 
which fossil organic bodies have undergone since 
they were first imbedded . in rocks, throw much 
hght on the consolidation of strata. Fossil i^ells 
in some modern deposits have been scarcely al«> 
tared, in . the coume; of centuri^ hav^ dio^plj^ 

£ 4 



m 



MHP1AUSA7I0H «f 



fftAU 



^I^PMK, pf:4bwr UiUaBl RMtjMT. But in-etbef 

tS^.itbtt sbieU iififtdia^ipeave^ mad left aa iavr 
pr^oBjO^y o{ it3 «xterior» or a caet of Jt» int«dnr 
^fuw^.'Pt^ tkirdly, a cast of the shell itadf, tW 
origiwl >patt^ of i^iicli has b^en Taaooved* 
^es^jdi&reat forms of fossUimtien may easily be 
gnd^too^ if we. examine ibe mud reMDlly thrown 
out from a pond or canal in whidi thwe areshellsf 
JS >ihe fnu(l be argilhceous, it acqaires-conedstenoy 
ffjB-.dryui^ and on breaking open a poitifwi of ic 
ii(^^i)d that ea^ shell has left imjwessip&s of its 
K^lerii^ fbrm. tf we theo remove the didl itself 
yi^ ^od within a solid nucleus of cky, having tfa^ 
^cm of the Interior of the Bbell. This form is 
oftsn.vecy di^^vent from that of the outer shdJ. 
fi^ffa a cast ^ch as «, Fig< 64.» commonly called 
a foasil screw, would never be sui^ected by aa 

,_ . Fif.St. .Fig. 55. 




mwpatMAaed concfaokigiBtto be theiutermd shape 
of 'die fossil anivUTO, t, F^.54. NorshmiM we 
iwK im^twd .at flat sight ditt tfarebdl a<«n4 



ioBiik' Tbe ^Mder urill obsen^ aft Ae fcHBJtoBaett^ 
tioiMd'figiife (i^'Fig; 6£k)y that ail emptjr 9<ftM 
jriiad^dark) iriitob the jAeS Jbe^onee oocnpted; 
Ufitwiiiterveiiies between the- eirrelopiiig 8tMi^<akid 
iJbe east of die innooth interior of the whoris. Ill 
such eases the shell has been dissolved and Ae 
poinpenest pardeles remoyed by^imter perodatmg 
tfafiirook* If the nucleus were taken out a hoBoW 
piould wonld remain^ on which the ^ttemal (ortti 
of the shell with its tubercles and strise, as seen 
in a» Fig. 55., would be seen embossed. Now if die 
qiaoe aUuded to between the nucleus and die im«* 
pressimi, instead of being left empty, has been 
filled up with calcareous spar, pyrites, or other 
mineral, we thai obtain from the mould an exact 
oast both of the external and int^nal form q€ the 
original shell* In this manner silicified casts of 
shells have been formed ; and if the mud or sand 
of the nucleus happen to be incoherent^ or sdhible 
in acid, we can then procure in flint an^ empty 
shell whi^ is the exact counterpart of the original. 
This cast may be compared to a bronze statue, 
representing merely the superficial form, and not 
the internal cHrganization ; but there is another 
description of petrifecdon by no means uncommon, 
and of a much more wonderfiil kind, wldicb'iisajf 
be^comparedi to certain anatomicsl moddis^ in wttx^^ 
whore not only ihe outward fofm» wad featuMtty 

E 5 • 



^t the nerf es, blood-vesacds, an^ oiber iotenul 
organs are alab ihown. Thus we find corsU, 
origmally calcareous, in triiich not only the |];eDeral 
shape, but also the minute and complicated internal 
organization are retained in flinL 

Such a process of petrifaction 'is still more re- 
markably eKhibited in fossil wood, in which we 
often perceive not only the rings of annual growth, 
but all the minute vessels and medullary rays. 
Many of the minute pores and fibres of plants* 
and even those ^iral vessels which in the living 
vegetable can only be discovered by the micro- 
scope, are preserved. Among many instances I 
may mention a fossil tree, seventy-two feet in 
length, found at Gosforth near Newcastle, in sand- 
stone strata associated wiili coal. By cutting 
a transverse slice so thin as to transmit li^t, and 
magnifying it about fif^-five times, the texture 
seen in Fig. 56. is exhibited. A texture equally 
minute and complicated has been observed in the 
SXg. se. wood of large trunks of fossil 

I trees found in the Craigleith 
} quarrynear Edinburgh, where 
stone was not in the 
I slightest degree siliceoos, bot 
! consisted chiefiy of carbonate 
i. (withHo.) of limc^ with oxide of iron, alu* 
mina, and carbon. In some examples the woody 
fibre is partially preserved« but it has entirdy 
vanished from others. . , 




Ch.l7J ORftAKIC BBaiAlini: AS 

In attempting to eqikun the proeeas of petri- 
&cuon in such cases, we may first assume that 
strata are rery generally permeated by water 
charged with minute portions of calcareous, sili- 
ceous, and other earths in solution. In what 
manner they become so impregnated will be after- 
wards considered. If an organic substance is 
exposed in the open air to the action of the sun 
and rain, it will in time putrefy, or be dissolved 
into its component elements, which consist chiefly 
of oxygen^ hydrogen, and carbon. These will 
readily be absorbed by the atmosphere or be 
washed away by rain, so that all vestiges of the 
dead animal or plant disappear. But if the same 
substances be submerged in water, they decompose 
more gradually ; and if buried in earth, still more 
slowly, as in the familiar example of wooden 
piles or other buried timber. Now, if as fast as 
each particle is set free by putre&ction in a fluid 
or gaseous state, a particle equally minute of car- 
bonate of lime, flint, or other mineral, is pre*' 
cipitated, we may imagine this inorganic matter 
to take the place just before left unoccupied by 
the organic molecule* 'in this manner a cast of 
die interior of certain vessels may first be taken^ 
and afterwards the walls of the same may decay 
and suffer a like transmutation. Yet when the 
whole is lapidified, it may hot form one homo* 
geneous npass of stone or metal* Spme of tb^ 

£ 6 



g)ir wttuauMAZAnav *of cmti^ 



oHgtaid' li^eoiiB) ossedtiS) or <M;lier oigafife^ #le« 
nueoto may ramttn mingled in oertain- ftMSrUt 
the lapidifying mineral itself may be so ciyslat* 
liaed in di£ferem ptatB as Co reflect light difer^illyi 
and thus the texture of the original body may be 
faithfuUy exhibited. 

r But the student will ask whether, on cheauea^ 
priaoqpks, we have reason to expect that mkieial 
matter will be thrown down precisely in thoae 
spots where organic decompoilition is in piogtess ? 
The following curious experiments may ser?e ta 
iUustPate this point. Prc^essor Goppert of Bret* 
IttU attempted rec^tly to imitate the natural pro? 
ee6» of petrifaction. For this purpose he steeped 
a variety of animal and yegetable substances in 
waters, some holding siliceous, others caleareons, 
oriiers metallic matter in solution. Hefeund that 
in the period of a few vreeke, or even dajis, the 
organic bodies thus immersed wei^ mineralized 
to* a ^certain extent* Thus, for example, thin 
vertical slices of deal, taken from the Scotch & 
f^Phtus 8yhestri8\ were inmiersed in a moderately 
Strong solution of sulphate of iron* When they 
had^ been thoroughly soaked in the liquid for 
several days, they w^e dried and ^qmeed to h 
fied^heat until the vegetable matter was burnt up 
and nothing remainedbut an oxide of iion, which 
was found to have taken the form of the deal so 
exactly that even the dotted vessels peculiar to 



o^m ' oBaAina moUHfa $( 



tUi» ftiafly^ of plttntsr aud jrcoeoiUitig; thme^jia 
f jig* Mn. w«Ke distinctly vosible . under tbe> micnhi 

Anodier ^cctdenlal. experiment, ha* been le** 
corded by. . Mr. Pepys . in the Geological TraJOo* 
actions. * An earthen pitcher containing ner^ni: 
qttarte of sulphate of inm had lemauied undifr* 
Qtrbed and unnoticed for about a twdvenionthiiii^ 
the JIaboratoiy. At the end of this time when dm 
li({iior wa» examined an oily af^pearance naa obn 
served on the 8ur£u^» and a yellowish powdeti 
which proved to be »ilphur, together wifbi a 
quantity of small hairs. At the bottom were di%- 
covered the bones of several mice in a aediment^ 
consistJiig of small grains of pyrit^ others, of suin 
pbur^ others of cryatallist^ groen sulphate, of mtqr^ 
aud a blucd^ muddy oxide of iron^ It was^^vidMt^ 
tliat some mice had accidentally been drowned ip. 
the fluid, and by the mutual actipn of. the anim^ 
matter and the sulphate of iron .on eacb.p^ery tlw 
metallic sulphate had been deprived of 4tEr oxjr^^p^ 
hence the pyrites and the other compounds., wei^ 
thrown down. Although the mice were jQot.jEb9» 
silized) or turned into pyrit^ the pheuQipeuqni 
shows bow nunenal waters» charged wit;)> sulpl^^ 
of iron, may be deoxydated.on cqping m contHet 
with animal matter uudergoiipg.putrefaQtioniuso 

* VoL i. p. 399. first series. 



8S IDHUAUZAIIOS OF tJhsUl, 

tbat atom after atom of pyritea may I>e ptedpitated^ 
and ready, under &voarable eircomstanoesi to 
replace the oxygen, hydrogen, and carbon into 
which the original body would be reiolved* 
' The late Dn Turner observes, that when mineral 
matter is in a << nascent state," that is to say, just 
liberated from a previous state of chemical com^ 
bination, it is most ready to unite with oth^ mat* 
ter, and form a new chemical compound. Probably 
the particles or atoms just set free are of extreme 
minuteness, and therefore move more freely, and 
are more ready to obey any impulse of chemioal 
affinity. Whatever be the cause it clearly follow% 
as before stated, that where organic matter newly 
imbedded in sediment is decomposing, there will 
chemical changes take place most actively* 

An analysis was lately made of the water whi<Ak 
was flowing oiFfiK)m the rich mud deposited by the 
Hooghly river in the Delta of the Ganges afW the 
annual inundation. This water was found to be 
hi^y charged with carbonic acid gas holding 
lime in solution. * Now if newly deposited mud 
is thus proved to be permeated by mineral matter 
in a state of solution, it is not difficult to perceive 
ihAt decomposing organic bodies, naturally im-^ 
bedded in sediment, may as readily become petri*^ 
fied as the substance artificiidly immersed by 
Professor Goppert in various fluid mixtures. 

* Piddington^ Asiat. Research, vol. xyiii. p. 226. 



.Cb.IV.] OBOAKK WtMAOtfL - ^ 

» 

It 18 ireU known that the ifater cdP springs, or 
that wluch is continuaUy percolating the eartVs 
emst^ is rarely free from a sligfat admisttnr^eidier 
of iron^ carbonate pf lime, sulphur^ flint, potash^ 
or BCHne other earthy, alkaline, or metallic ingre- 
dient Hot springs in particular are copiously 
charged with one or more of thede elements ; and 
it is only in their waters that silex is found in 
abundance. In certain cases, therefore, especially 
in vcdcanic r^ons, we may imagine the flint 
of silidfied wood and corals to have been sup- 
plied by the waters of thermal springs. In other 
instances, as in tripoli and chalk-flint, it may 
haTe been derived in great part, if not wholly, 
from the decomposition of infusoria, sponges, and 
other bodies*. But eren if this be granted, we 
have still to inquire whence a lake or the ocean 
(Ban be constantly replenished with the siliceous 
tnatter so abundantly withdrawn from it by the 
secretions of these zoophjrtes. 

In regard to carbonate of lime there is no 
difficulty, because not only are calcareous springs 
Very numerous, but even rain-water has the power 
of dissolving a nrinute portion of the calcareous 
rocks over which it flows. Hence marine corals 
and mollusca may be provided by rivers with th^ 
materials of their shells and solid supports. But 
pure silex, even when reduced to the finest powder 
and bpiled, is insoluble in water. Netertheless 



30^ FLINT w m4fmm» -iimsils, gf^ % , 

widftly cpri^ad ias ai\^ the ^p«^c jxx^ . wli«^. 
femasolai:^ fi prop0iMio», of tJieiYokaoici. j^uloiiic|. 
aod-mietaiQQrpbio ropk^, and ai^. tlifirefojre^^imit'. 
vQfBul, occurring ^omewh^se la the cQvam of everiy! 
large river. -, i, ., 

> Ulie silkeous «atth, which eonBtitiites laare.ilita 
h|d£. the bulk of felspar, is intuiialelycoiiibined 
with ahvDiine^ potash^ and some other elements^ 
•The aUoaline matter of the fekpar has a efaemicdi 
aflSnily for water^as also for the carbonic :acid 
whieb.is more or less contained in tlie:watecB. of 
most^ springs. The water therefiMre carries away 
aJkatine matter, and leaves behind a day coosislang 
o£ . alumme and flint. But . this residue . of. the 
dfiGomposed mineral, which in its purest state: is 
called. poroelain-K^y, is found to contaia only, a 
sDiall proportion of the silica which existed in the 
oxiginal. felspar. The other part ther^ore must 
hav)e been dissolved^ and removed; and thia caa.be 
accounted foir in two ways, first, because silex. whoa 
combined, with an alkali m soluble in water; 
secondly, because silex in what is technically calkid 
ita nasc^it state is also soluble in water. Hdice 

■ 

an endless suiqpily of ^ca isiaiforded to^the watars 
.of the sea. 

* Jam. Ed. l^ew Phil. Joiirti. NV>. 30. p. ^46. 



aLtt.j - -^i0if^£K<tt DSlmrM. Qflfr 



Wiiich emci^ Ifti^gely into the ^<]inpo9itioii' of 
^nuHle' atnd various sandBCOnes,' may yield iilea:* 
wUbb may be dissolved in water^ for nearly hidf 
of thiiK minieral consiflte of silica, combined with' 
ahimine, potash, and ^out a tenth part bf ir6i& 
The o:dda€ion of this iron in the air is die prin* 
cipal cause of the waste of mica. 

We faarre still, howe?er, much to learn before 
the cotnversion of fossil bodies into stone is fully* 
miderstood. Scnne phenomena seaoa to imply that 
the mineralization must proceed with consid^ able 
rapidityv ^ stems of a soft and sueculent diaractery 
and of a snost perishable nature, are preserved in 
flint ; and there are instances of the complete stli« 
cifioation of the young leaves of a palm-^tvee wli^ 
justaboiit to shoot forth, and in that state which 
in the West Indies is called the cabbi^e of 'the 
palm.* It may, however, be questioned whether 
in such cases there m^ not have been sqme antiM^ 
septic quality in the water which retarded piMErei^f * 
tnm, so that the soft parts of the buried -substtao^* 
may have remained for a long time without dis^^ 
integimion, like the flesh of bodies itnbe^edki.^ 
pest , .c 

•Mr. Stokes has pointed out exaiiipfes of petrl«% 
fiM!(ti(nis ia whieh the more peri^mbl^ «i^ otkenii 

♦ StofcQj, GeQl. Trans, vol. v, p» 2,1.?^ sepon^ f^nss. 



M psodBss 0r nsnEffActioxi; c^sBtL 

fibere the more durable portieiis of wood are 
j^^sen^ed* Tliese Toriadons, he sBggesitB, must 
doabdesB depend mi die time when the lapidifying 
minetal was introdoeed. TkxiB in certain mlicified 
stems of pahn^^trees die cdlnlar tissue, that most 
destructible part, is in good oondition, all signs of 
the bard woody fibre haying disappeared, and the 
spaces once occupied by it being hollow or filled 
with agate. Here petrifiiction must have com- 
menced soon after the wood was exposed to the 
action of moisture, and the supply of mineral 
matter must have fidled, or the water have become 
too mudi diluted before the woody fibre decayed. 
But when the latter is alcme discoTerable^ we must 
then suppose that an interval o£ time elapsed 
before the commencement of lapidification, during 
whidi the cellular tissue was oUiterated. When 
both structures, namely the cellular and the 
woody fibre, are preserved, the process must have 
commenced at an early period, and continued 

without interruption till it was ccmipleted throng- 
out* 

* Stokes^ GeoL Tnms. vol. v. p. 213. second series. 



M 



CHAJPTEE V. 

l&LETATION OF STRATA ABOTE THE SEA — HORIZONTAL 
AND INCLINED STRATIflCATIOW. 

Why the elevated position of marine strata should be re-* 
ferred to the rising up of the land, not to the going down 
of the sea— Upheaval of extensive masses of horizontal 

• atrata-^ Inclined and vertical stratification — Aoticlniai 
and synclinal lines — Examples of bent strata in east of 
Scotland — Theory of folding by lateral movement — Dip 

' and strike — Structure of the Jura — Rocks broken by 

, flexure'-* inverted position of dbtiirbed strata-*- Unecm* 
formable stratification — Fractures of strata — Polished 
surfaces — Faults — Appearance of repeated alternations 

' produced by them — Origin of great faults. 

1 * 

Land has been raised^ not the sea lowered. --^ It has 
been already stated diat the aqiieous rocks can- 
taining marine fossils extend over wi^ continental 
tracts, and are seen in mountain chains, rising to 
great heights above the level of the sea. Hence 
it follows that what is now dry land was otioe 
under water. But if we admit this conclusion we 
must imagine either that there has been a general 
lowering of the waters of the ocean, or that the 
sdid rocks, once cov^ed by water, have been raised 
up bodily out of the sea, and have thus become 
dry land* The earlier geologists, finding them« 
selves reduced to this alternative, embraced the* 



OS XAKD HAS JHKS SA1BBD, fTtaiU 

fblnor- t«pinaoii, assmmng diat die ocean wm 
grigknUy' unweroaly ft&d had gradually sunk dewn 
1}o4tsi actual lerel^ so that the present islands and 
cioiitiiieDts were left dry. It se^^med to them fkf 
e^er to <tonoeive that the water had gone down^ 
thun that solid land had risen upwards inio iti 
present position. It was, however, impossible to 
invent any satisfactory hypothesii^ to explain the 
disappearance of so enormous a body of water 
throughout the globe, it being neoessairy to infer 
Aat the ocean had once stood at whatever height 
mairine shells were detected. It moreover ap« 
peared clear, bA the science of Geology, advanced, 
that certain spaces on the globe had been altera 
iHUely sea, then land, then estuary, then sea again, 
and, lastly, onoe more habitable land, lumng re« 
^iiain^in eaeh-of these states for considerable 
p^ripda. In order to account for such phsucN 
laena, . without admitting . any movennsit of the 
\md. itselfj we are required to imagine se^veiiai 
ri^eats a«9id retums.of the ocean ; and ev^oi dien 
our theory applies merely to cases where the 
ipciuriiie' 9tnata composing the dry land are hori-» 
^ontal) leaving unexplained those more commcm 
ifi»tmeefi where strata are inclined, curved^ 4>r 
(Med on their, edges, ai¥l . evidently not in the 
position in which they were first deposited, 
. I G^logists^. thecefinre, were at last compelled to 
bw reooursQ to the other alternative^ namely, the 



doctrine> diat ijie solid land- lias heBhtepetMbf 
jmv^ upwards or down^vaids, so as penttaaendy 
io< chatage its position relatiinely to the sea. Thevft 
ai^e sev^al distinct groundft fca prefemog this 
ooBckision* Firsts it will account eqaaMj for the 
posidon of those elevated masaes of marine origin 
in which the stratification remains horisEOOtal, and 
for those in which the strata ore cBstnrbed, broken; 
inclined, or verticals Secondly, it is oonwteift 
with human experience that land should ' riiete 
gradually in some places and be depressed ih 
others^ Such changes have actually oeci^rn^ in 
our own days, and are now in process, being 
aceonipanied in some cases by violent convulsion^ 
while in others they proceed insensibly, or «H& 
only ascertainable by the most careful scientific 
observations. On the other hand, there is no etd^ 
denee from human e3q)erience of a low^*ing of 
ihe sea's level in any region, and the' wat^fs <tf 
the ocean cannot sink in one place without theii* 
level being depressed everywhere throo^ottt'tfije 
globe. 

These preliminary remarks will ja^pare the 
reader to understand the grejittheopetieal interest 
attaehed to all facts connected with th^ position ttf 
sfttita, whether horiasofital or inclined,^ curved tnt 

vertical. " ' ^ ' ' •' 

Now the: fix»t and most sampW appearance? i^ 

wfaerfi stiBijSL of marine origin oecauc abawe^tbe h^ 



94 MMB HAS MEN BAIiBE^ fTM^ 

•f the fai in korkofitid' pofidon*' Sileh a»e tbe 
ftrata wlueh we meet with in the go«th of ^eilyi 
filled with shdis of the same speeies a» wnw lire 
in the Medhenranean. Some of these rodas rise 
to the haght of 2000 feet and more above the 
aea. Other mountain masses might be mentioned 
with hoiixontal strata ef high antiquity which eon* 
tain fossils whcUy dissimilar in form to any now 
known to esdst, as in the south of Sweden^ near 
Lake Wener, where the beds of a deposit) called 
Trmsition or Silurian by geologists, occur in as 
level a position as if they had recently fimned 
pan of the ddta of a great river, and beai left 
dry on the retiring eS the annual floods. Aqueous 
roeks of about the same age extend over the 
lake-district of North America, exhibitii^ in Kke 
manner a stratification nearly undisturbed* The 
Table Mountain at theCape of Grood Hope is an*- 
other example of highly devated and perfectly horir 
zontal strata, no less than 3500 feet in thickness^ 
and consisting of sandstone of very ancient data. 

Instead of imagining that such fossili£»t»us 
rocks were always at their present levdl, and that 
the sea was once high enough to cover them, we 
suppose them to have constituted the ancient bed 
of the ocean, and that they were gradually up» 
lifted to their present height. This idea, how- 
ever startling it may at first appear, is quite in 
accordance, as above stated, with the saasiogy of 



ClkVa l^KT TBB SKA I/>Wl»Ea ' fft 

chaogeB norsr gomg oa in eertam te^piooB of the 
gipbe. Thrift in pacts of Sweden^ for em— yfai 
uod the shoreaand isUnds of the Gulf of Satfaiiia» 
proo& have been obtained Uiat the land is ck» 
periencing» and has experienced finr oenturie^ a 
slow upheaving movement Playiair argued in 
&vour of this opinion in 1802, and in 1807 Yon 
Buchy after his travels in Scandinavia^ announced 
his convictum that a rising of the land was in 
progress. Celsius and other Swedish writers had^ 
a centiiry before, declared their belief that a 
gradual chai]^e had for ages been taking place 
in the relative level of land and sea. They attri^ 
buted the change to a &11 of the waters both of 
ibe ocean and the Baltic; but this theory has 
now been refiited by abundant evidence ; for the 
alterati(Mi of relative level has neither be^i unb- 
versal nor everywhere uniform in quantity, bojt 
has amounted in some regions to several feet in 
a century, in others to a few inches^ while in thf 
southernmost part of Sweden, or the province of 
Scania^ there has been actually a loss instead 
of a gain of land, buildings having gradually 
sunk below the level of the sea. * 

* In the first three editions of my Principles of Geology, 
I expressed many doabts as to the validity of the alleged 
proofs of a gradual rise of land in Sweden; but after visiting 
that country in 1834 I retracted these objections, and pub- 
lished a detailed statement of the observations which led me 
to alter my opinion in the Phil. Trans. 1835, Part L See 
also Principles, 4th and 5th editions, bookii. chap." 17. 



It fffpem from tbe dbservniiom of Mr. Dannai 
food ocbers than very extensive i^kms of tbe cs«ii» 
tineiit of South America have |)een wadeaigomg 
dow and gradual upheaval, by which tbe .Imni 
plaiitf of Patagonia, cov^^ with leoait marine 
shells, and the Pampas of Buenos Ajres have been 
formed. * On the other hand the gradual smkiiig 
of part of the west coast of Greasland, for ihe 
space of more than 600 miles from north to soud^ 
during the last four centuries, has been established 
by the observations of a Danish naturalist^ Dh 
Fiiigel. And while these proo& of continental 
elevation and subsidence by slow and insensible 
movements have been recently brought to light, 
the evidence is daily strengthened of continued 
changes of level effected by violent convulsions in 
-countries where earthquakes are frequent. Here 
the rocks are rent from time to time^ and heaved 
up or thrown down several feet at once, and dis- 
turbed in such a manner, that the original position 
of strata may, in the course of centuries, be mo- 
dified to any amount. 

It has also been shown by Mr. Darwin, that, in 
those seas where circular coral islands abound, 
there is a slow and continued sinking of the sub- 
marine mountains on which these masses of coral 
are based; while in other areas of the South Sea, 
where coral is found above the sea level,* and in 

* See his Journal in Voyage of the Beagle. 



(A.^ ta^^'AmBiskm^^ of land. 97 

jiSSS^«Ltim\i6n«i ^^^ where there aire lio cfrciuar 
(jFfettrffer re^ Ae land is on the rise.* 
^W w6tdf reqiiire a volume to explain to the 
reaiSer 'flie vafioiis facts and phenomena which 
6iffifiM ffie reality of these movements of land^ 
"^fSeitiet bf elevation or depression, whether accom-» 
j«imOT by earthquakes or accomplished slowly and 
VfAont local disturbance. Having treated fully 
oftKese subjects in the Principles of Geology, I must 
assume, in the present work, that such changes 
are part of the actual course of nature ; and when, 
admitted, they will be found to afford a key to the 
interpretation of a variety of geological appear- 
ances, such as the elevation of horizontal or 
disturbed marine strata, the superposition of 
freshwater to marine deposits, and many other 
phenomena, afterwards to be described. It will 
also appear, in the second part of this volimie, how 
much light the doctrine of a continued subsidence 
of land may throw on the manner in which a series 
of strata formed in shallow water may have accu- 
mulated to a great thickness. The excavation of 
vaDeys also, and other effects of denudation, of which 
I shall presently treat, can alone be understood 
when we duly appreciate the proofs now on record 
of the prolonged rising and sinking of land through- 
out wide areas. 

* Proceedings of Geol. Soc. No. 51, p. 552., and hia 
Journal in Voyage of the Beagle, vol. iii. p. 557. 



99 



VEBTICAL, IKCLIKl^^ AKB 



I^artL, 



Fig. 57. 



Jjiclined strtxttfieaiion^ — The JUQSt uiv^uiypcal 
evidence of a change ia the ordinal position of 
strata is afforded by thei|r standing v]f perpen- 
dicularly on their edges, which is by no means a 
rare phenomenon, especiaUy in mountainous coun-* 
tries. Thus we find in Scotland, on the southern, 
skirts of the Grampians, beds of puddingstone 
alternating with thin layers of fine oand, all placed 
vertically to the horizon. When Saussure first 
observed certain conglomerates in a similar posi-> 
tion in the Swiss Alps, he remarked that the 

pebbles, being for the 
most part of an oval 
shape, had their longer 
axes parallel to the 
planes of stratification, 
(See fig. 57.) From 

reriicaiconglomerale ana sandstone, ^j^ j^^ inferred that 

such strata must, at first, have been horizontal, 
each oval pebble having originally settled at the 
bottom of the water, with its longer side parallel 
to the horizon, for the same reason that an egg 
will not stand on either end if unsupported. Some 
few, indeed, of the rounded stones in a conglo- 
merate may afford exertions to the above rule, 
for the same reason that we see on a shingle beach 
an occasional oval or flat-sided pebble Testing on 
its end or edge. For some pebbles having been 
forced along the bottom and against each other, 
may have settled in this position. 




Ch.V5 



CUKVSD STRAZIFiGjBnoX. 



M 




Vintical strata, when 
liiey oan be traced Gonr 
tinuQudy upwards or 
downwards for some 
depth, are alxaost inr 
vatf-iably seen to be 
parts of great curvefl^ 
wbicb may have a diaf- 
meter of a few yard^^ 
or of several miles. I 
shall first d€iscribe twp 
1 1 curves of considerable 
regularity, which occur 
in Fprfarshire, extendr 
ing over a country 
i twenty miles in breadth, 
llfrom the foot of the 
s> Grampians to the se^ 
near Arbroath. 

The mass of strata 
here shown may bei 
nearly 2000 feet in 
thicjkness, consisting of 
red and white sand* 
stone, and various co- 
loured shales, the beds 
being distinguishable 
into four principal 
groups, namely, No. 1, 

F 2 



Ired mipaAu^x ebale; Na 8.. red sipdstoin.^ losed 
S^r b«il4ii)g9 No. d« conglomerate ; and No.; 4^ 
grey, paving'-i^tDne, and tile-stone, with green 
4nd. reddish shale^ containing peculiar organic 
jnemauig. A glance at the section will show that 
aeach'of the formations % 3, 4^ are repeatai 
thrice at the surface, twice with a southerly and 
oiioe with a northerly inclination or dtp, aj^d. the 
beids in No, 1., which are nearly horizontal, are 
atiU brought up twice by a slight curvature to the 
surface, once on each side of A. Beginning at the 
north-west extremity, the tile-stones and conglo- 
merates No. 4. and No. 3. are vertical, and they 
genially form a ridge parallel to the southern 
fiifcirts of the Grampians, The superior strata Nos. 
2. and 1. become less and less inclined on descend- 
ing to the valley of Strathmore, where the strata, 
having a concave bend, are said by geologists to lie 
in a " trough " or " basin." Through the centre of 
this valley runs an imaginary line A, called techni- 
cally a " synclinal line," where the beds, which are 
tilted in opposite directions, may be supposed to 
meet It is most important for the observer to mark 
fiuch lines, for he will perceive by the diagram, 
that in travelling from die north to the centre jof 
'" the basin, he is always passing from older to newer 
bedsi; whereas after crossing the line A, and pur- 
suing his course in the same southerly direc^on, 
he is continually leaving the newer, and advancing 



CUHVEli STRATA, 



m 



upon older str&ta. AU ihe depo^ ii4ii(^')i« bad 
li«fi>re examined begin tlien to ' near in K^ 
T^rsed order, until he arrires at the centtul astiii 
of die . Sidlaw' hjlb, where the strata are seat' M> 
foiman arch or saddle, hdviAg im aBtidiNai)iaie^ 
B, in the centre. On passing this line, and con- 
tiiiuing towards the S. E.^ the formations 4, 8, 
and 2, are again repeated, in the same relative 
order of superposition, hut with a northeHy dip. 
At Whiteness (see diagram) it will be seen diat 
die inclined strata are covered by a newer de- 
posit, a, in horizontal beds. These are composed 
of red conglomerate and sand, and are newer than 
any of the groups, 1, 2, 3, 4, before described, and 
rest ummfonmMif upon strata of the sand-^tone 
group, No. 2. 

An example of ctu-ved strata, in which the bends 
or convolutions of the rock are shsrpdr and brnuve 
numerous within an equal space, haa been well 




102 ExpERiifEirrB to IUUTSTRATE ^int t 

described by Sir James HaU. * It occurs Hesif 
St. Abb's Head, on the east coast of Scotland, wh^re 
the rocks consist principally of a blUish dttte, 
having frequently a ripple-marked sur&ce. The 
Vndulations of the beds reach from t&e top td die 
bottom of cli£& from 200 to 300 feet in height^ 
9nd there are sixteen distinct bendings in the 
eourse of about six miles, the curvatiiffes b^g 
altematdiy concave and convex upwards. 
: An eiq>eriment was made by Sir James Hall, 
with a view of illustrating the manner in which 
such strata, assuming tfiem to have been originally 
horizontal, may have been forced into their jn-e-* 
^ent position. A set of layers of day were placed 
under a weight, and their opposite ends pressed 
towards each other with such force as to eau$e 
them to approach mbre nearly together* Oi^ the 
removal of the weight, llie layers of day were 
found to be curved Bud folded, so as to bear H 
miniature resemblance to the strata in the cliffii. 
We must, however, bear in mind, that in the 
natural section or sesr^liff we only see the foldings 
imperfectly. One part being invisible beneath the 
sea, and the other, or upper portion, being sup- 
posed to have been carried away by denudation, 
or that action of water which will be explained in 
the next chapter. The dark lines in the accom- 

• Edui. Trans, vol. vii. pi. 3. 



CK v.] CUItVED STBATjt. iQS 

panjiag plan (Fig. 60.), represent what is actually 
seen of the strata in part of the line erf" cliff alluded 
to ; the f^Dter lines, that portion which is conceded 
beiteath the sea level, as also that which is sup- 
Fig 60 




posed to have once existed above the present sui- 
Jace. 

We may still more easily illustrate the effects 

which a lateral thrust might produce on flexible 

strata, by placing several pieces of differently 

Rg. 61. 




eoloored clodia upon a table, and when they are 

spread out horizontally, cover ihera with a book. 

?hen apply other books to each end, and fcrce 

F 4 



1^ ORIGI)^ jCW^OTYSJI^ 9I9ATA. CP«iU 

l^t^;,^ esm^ ia^ts^tboa^ of .4i)«. toil 9ti8tB«; 

• t . To. in^Hir^ 3¥hether the fOi^lpgKHis - fle^iupei iit 
strain have really been due to simUar sidewEj- 
i^ovementSy or other exertions of fori^ would lefMl 
me. farther into the regions of speculation and. 
Gpnjeeture than might be consistent with the 8C(^ 
of this elementary w(»rk. When the volcajqic and 
granitic rocks aredescribed, it will be seen that sobv^ 
of them havcy when melted, been injected forciUy 
into fissures, while others, already in a solid states, 
have been protruded upwards through the incum-> 
bent .crust of the earth, by which a great dis-^ 
placement of flexible strata must have been caused. 
It also appears that cavities are sometimes formed 
in the interior . of the earth, whether by the re- 
moved of matter by volcanic action, or by the con- 
traction of argillaceous rocks, or other causes. In 
this manner pliable beds sinking down, from &ilure 
of support, into chasms of less horizontal extent, 
may have become folded and compressed laterally. 
Such subsidences have been witnessed on a small 
scale in the undermined ground immediately over 
coal-pits, l&om which large <}uantities of coal and 
stone had been extracted* 

Between die layers of shale, accompanying coaI» 
we sometimes see the leaves of fossil ferns spread 
out as r^ularly as dried plants between sheets of 



1m*iIi ttrfrowfe, mast hate- rested hwu(Hi tally en 
soft mud, when first d^oaited. I^ tfaerefefr^ 
theynsd ibe layers of shale ape now indmed,'or 
Stasdiiig <m end, it is obriooBly the efiect of siA> 
sequent deraBgement. ^^^e proof becomes, If 
pOBuble, BtUl more Btriking wh^i these strata, in- 
cktdiDg vegetable remains, are curved again and 
again, and even folded into the form of the letter 
Z, M that the same continuouB layer of coal ia cut 
through several times in the same perpendicular 
shift, Thus, in the coal-^eld near Mens, in Bel- 

Tig. 62. 




ginm, these zigzag bendings are repeated four or 
five times, in the manner represented in Fig. 62., 
ibe black lines representing seams of coal. • 
Dip and Strike. — In the above remarks seve- 

• See plan by M. Chevaliw, Burafs D'AubuUson, torn, u: 
P.3S4. 



■n ^». 


Ptg.63^ 


_N 




m 




^ 




Sea Level K 


>^ 



fal technical texifid Ka^ci lysd^tt fiy^ stkiili &s' i%^ 
A^ unetmpmahb pdgitfm of Mltt^ ffi»d tiiroiWP 
^lAo; aind gyndinci Ikies^ \«ibidhy as weft' dsfKe 
^rn4« of the beds, I shall now expiaiit If A A!f%H 
turn or bed of I'ocic, instead of being quite levels 
1^ inclined to one side; it is said to dip i iSati poiK^ 
. of the compass to which it is indined b called tile 
foiyU of dipf and the degree of defritttibn from* A 
level or horizontal line is caBed ike amouai ofdipf 

or the aiyh ofdip^ 
Thus, in the an^ 
nexed diagMm 
(Fig. 63.)j a se- 
ries df strata are 
inclined, and they dip to the north at an angle of 
forty-five degrees. The strike ^ ot line of beartj^j 
is the prolongation or extension of the strata in a 
direction at right cmgles to the dip ; and hence it i$ 
sometimes called the direction of the strata* Thus^ 
in the above instance of strata dipping to the 
north, their strike must necessarily be east and 
west We have borrowed the word from the 
German geologists, streichen signifying to extend, 
to have a certain direction. Dip and strike may 
be apUy illustrated by a row of houses running 
east and west, the long ridge of the roof represent- 
ing the strike of the stratum of slates, which dip 
on one side to the north, and on the other to the 
south. 



eii.T.i . DIP an6 strikk 107 

A stratum which is horizoDtal^ or quite level in 
all directions, has neither dip nor strike. 

It is always important for the geologist, who is 
^ideaVonring to comprehend the structure of a 
country, to learn how the beds dip in every part 
of the district j[ hut it requires some practice to 
avoid being occasionally deceived, both as to the 
point of dip and the amount of it. 

If the tipper surface of at hard stony stratum 
be uncovered, whether artificially in a quarry, or 
by the waves i^ the foot of a el^. it is easy to 
determine towards what point of the compass the 
slope is steepest, or in what direction water 
would flow, if poured upon it. This is the true 
dip. Perfectly horizontal lines in the face of a 
vertical cliff may be the edges of highly inclined 
strata, if the observer see them in the line of their 
strSce, their dip being inwards from the &ce of 
the cliff. If,, however, we come to a break in 
the cliD^ which exhibits a sectio(n exactly at right 
imgles to the line of the strike, we are then able 
to ascertain the true dip. In the annexed (frawing 
(Fig. 64.)y y^e may sup{K)se a headland, one side 
et whidb faeces to the north, where the beds would 
appear perfectly horizontal, to a person in the 
boat; while in the other side facmg the west, the 
frae di^ would be seen by the person on shore 
to be ift an an^e of 40^. li^ therefore, our ob- 
servations are confined to a vertical precipice facing 

t 6 



W)8? 




in one direction, we must endeavour to find a ledge 
or portion of the plane of one of the beds pro- 
jecting beyond the others, in order to ascertain 
die true dip. 

It is rarely important to determine the angle <^ 
incdination with such minuteness as to require the 
aid of liie instrument called a clinometer. We 
1%. 63. may measure the anj^e 

vithin a few degrees by 
standing exactly opposite 
to a cliff where the true 
dip is exhibited, holding 
the hsLuds immediately 
before the eyes, and' 
; placing the fingersof one 
in a perpendicular, and 
of the other in a horizontal posiuon, as in Fig. 65. 
It is thus easy to discover whether the lines 




Ch.V.] pi? lEtD STRIKB, 10^ 

of the inclined beds biaeet the angle of 90°, 
formed by the meeting of the hands, so ae to 
give an angle of 45°, or whether it would divide 
the space into two equal or unequal portions. The 
upper dotted line ii)ay express a stratum dipping 
to die north ; but sliould the beds dip precisely to 
the oppoaitc point of the compass as in the lower 
dotted line, it will be seen that the amount of in- 
clination may still be measured by the hands with 
equal iacility. 

It has been already seen, in describing the 
curved strata on die east coast of Scodand, ii^ 
Forfarshire and Berwickshire, that a series of 
concave and convex hendings are occasionally 
repeated several times. These usually form part 
of a series of parallel waves of strata, whiohare 
prolonged in the same direction throughout a con~ 
siderable extent of country. Thus, for example, in 
the Swiss Jura, that loftjr ch^n of mountains has 
been proved to consist of many parallel ridges, 
with intervening longitudinal valleys, as in Fig. 66., 
the ridges being formed by curved fossiliferous. 
strata, of which the nature and dip are occasionally 
displayed in deep transverse gorges, called " cluses," 
caused by fractures at right angles to the direction, 
of the chwn.* Now let us suppose these ridges 

• See M. Thunnann'B work, " Essai aur les SouUvemeng 
Jnnssiquea du Porrentniy, Paris, 1838," with wttom I es- 
smined part of these mountains in 1835. 




Siclim iUtulratliv He •tmclmr gf Ihr 5iciu Jura. 

and parallel valleys to run north and south, we 
should then say tfiat the ^rike of the beds is 
dordi and south, and the (Rp east and -west. A 
Ene drawn along the summit of llie ridges A, B 
trould be an anticlinal line, and one following ^e 
bottom of tile adjoining valleys a synclinal line. 
It will' be observed that some of these ridges, A, B, 
6re' unbroken on die summit, whereas one of them, 
C has been fractured along the line of strike, 
And a portion of it carried away by denudation, 
ft) Aat the edges of the beds in the formatioh^ 
OibiC (!0Die oat to &e day, ot, as the miners say, 
vtop OfA, on the sides of a valley, the gtoun^ 
plan of sudl & denuded ridge as C may be ex- 
ptetaed by the diagram Fig. 67., and the cTosS 
section of the same by Fig. 68. The line D E, 
Fig. 67., is the antklinid line^ on each side of 
which the dip is in opposite directions^ as expressed 



A. YS AMT^tlKUkt^ AH^ (rhUOtt^Ah &KE& 



HI 



1%. 67. 

jjwv.ifw f r II I I 



Fi^t €fh 




»>> > ■ > 





Gfomd^ptiUk^t^ tkB ttmHUied nidge e^Jig, 66. 

by the arrows. The emergence of strata at the 
surface is called by miners their outcrop or basset* 

If, instead of being folded into parallel ridgeSf 
the beds form a boss or dome-shaped protuberance^ 
and if we suppose the summit of the dome carried 
off, ^e gifound plan would exhibit the edges t^ 
ibe stifaxa forming a succession of circles, or el-' 
lip^es, round a^ e<»nmon centre. These cities a)*e 
the Maes of strike^ a*nd the dip being always at 
i^ht aisles isf inclined m the course of Acr cif -* 
euit to every point of the compass^ eonslilxitii^ 
#hat is termed' an qua^qwt^versai dSp'-*-that H 
Mrfting each way; 

In the js^ajority of cases^ an anticlinal asis forms* 

a ridge, anda synclinal teis- a vaHey, as in A, B", 

Fig. 58i p. 991 ; but fliere are exceptions to thisr 

Fig. 69. TvSe, the be<fe sOmetbheST 

sloping iilwards' ft'om eit&ei^ 
side of £1- ilnountai]^^ a^ 'vt^ 
\fig. m. 

On following ibe sintieli-r 
'nal line of the ridges of ^ 




IIS 



SENT .aXKATA^ J^ PYlUBl^EEa 



ilfvtli 



Jum, befQm jnf^ti^nad, At B» Q Fig. 66.9 we 
ofteci^ dkeoKrer ipngijljudinal fissures alo^g tbe 
line wiiisre .the flexure n^oft greatest. At die 
eastara esKtirermty. of the Pyrenees a curious illus- 
tration 1 o£ an analpgous phenomenon may be 
seen on. a small scale (Fig. 70.)« The strata 
there laid open, in the sea-diffi, consist of marl, 

Fig. 70. 




fUrat0 qf chert, fpii, and marl^ neur Si. Jean de X««. 

grit, and chert, belonging to a formation o£ 
the age of the greennsand of Ei^lish geologists^' 
Socne of the, holdings are so sharp, that frag- 
ments, of the slaty chert— * a hard flinty rock—-* 
takm from the points where they form anao^e at 
a, mi^t be used for ridge-tiles on the roof of a 
house. Although this chert is now brittle, we 
must necessarily suppose that it was flexible when 
folded into this shape ; nevertheless it must have 
had seme aolidily, for precisely at the angle of 
fl^oire there are niun^ous cracks filled with calce- 
dony.. There are, also some veins of quarti, i. 
Fig* '70.9 • traversing the same formation, which 
hav« fiBed irregular fissures, probably enfiltered at 
the same time as th^ calcedony above mentioned^ 
. Betivi»9l, San:Cateriii% and Castregiovann^ in 
Sieily, b^it and undulatuig gypseous marls occur, 



eh. V.) 



SBVBBBED DIP CV flTRATA. 



ua 



widi h^e and diere diin beds of solid gypsum 

inierstratified* Sometimes these solid lajers ha^e 

been Iffoken into detaehed fragments, still pre* 

Fig. 71. sening their riuurp edges, 

{ffffy F^. 71.)> while the 
continuity of the more 
pliable and ductile marls, 
m nij has not been inter^ 
rupted. 

I shall conclude my 




m, marl. 



remarks on bent strata by stating, that, in moun^ 
tainous regions like die Alps, it is often difficult 
for an eatperienced geologist to determine cor-« 
reedy the relative age of beds by superposition, 
so often have the strata been folded back vtpoti 
themselyes, the upper parts of the curve having' 
been removed by denudation. Thus, if we met 
with the strata seen in the section Fig. 72., we 
should naturally suppose that there were twdve 
Fig, 72. distinct beds, oi^ sets of 

r-^..,^^^^-^^^^^ beds, No. 1. bexag the 
By)y)\;9y^5yiw^ youngest, and Nix 12. 

the oldest of the series. 
But diis section may, perhaps, exhibit merely six 
beds, which have been folded in the manner seen 
in Fig. 73., so that each of diem are twice re* 
peated, the position of one half being reversed, 
and part of No. 1., originally the upparmost^ 
having now become the lowest of the series* 



114 CURVES STRATA IN THB AtfS. 

K& 78. 




These phenomena are often observable on a mag- 
nificent scale in certain regions in Switzerland, 
where there are precipices from 2000 to 3000 
feet in perpendicular heighL In the Iselten Alp, 
in the valley of tha Lutachlne, between Unterseen 
9ad Grindelwald, curves of calcareous shale are 
from 1000 to 1500 feet in height, in which 




iSA be(fa SontetSmBs plunge down verticaHy for a 
depth-of KlOO^t and more, before they bend rounct 



CII.V.] UNCONFOKVABKE SVSimfMrATION. I|j 

again. Theve are maAy flexaretf not inferior te 
dimensions in the Pyrenees, as those near Gravamiey 
ait the base of Mont Perdu. 

Uncariformable sirai^ficaiion* *-* Strata are siuid 
to be nnconfonnable, when one series is so placed 
over another^ that the planes of the superior re- 
pose on the edges of the inferior. In this case 
it is evident that a period had elapsed between 
the production of the two sets of strata, and 
diat, during this interval, the inferior series 
had been tilted aiid disturbed.r Afterwards the 
upper series was thrown down in horizontal stretta 
upon it* If these superior beds are also inclined, 
it is plain that the lower strata have been twice 
displaced ; first, when they were themselves brought 
into an inclined position, and a secofid tittie when 
the superior beds were thrown out of th6 hori- 
xontal line. 

It often ha{)pen& that in the inteihral between 
the depositi(»i of two s6ts of unconformable strata, 
the inferior rock has been denuded, and soihetalttiesi 
drilled by perforating shells. Thus, for escample^ 
at Autreppe and Gusigny^ £rear ]M£ons, beds of 
ancient ^Um^ <iommonly called transition lim^ 
stimoy highly incUned, and often bent, are covei^ 
with horizontal strftlstr of gl«eiiish c^d ^hi<^idi J^nialrk 
of die etetaeeotts formation, wln<^k will be mentioned 
inaffieitareeha)^r« Tke lowest aziel therein ^ 
oldest be^fj^ hcnrisdntal series is usijally thesMd 



\lf rtBBuaxa nr strata. [PtetL 

yHd ttrnghmethte, a, m wUck are rounded frag- 

Fig. 75. 






allots of stone^froin an inch to two feet in diameter. 
These fragments have oftrai ac&ering shells at-* 
taobed to them, and have been bored by perfor-« 
atiiig mollusea; The solid stff&ce of the infa^or 
limestone has also been bored, so as to exhibit 
Qrlindrioal and pear-shaped cavities, as at e, the 
work of saxicavous moflusca; and many rents, as 
at by which descend several feet or yards into the 
limestone, have been filkd with sand and shells^ 
similar to those in the stratwn cu 

Frojctures of the strata. — Numerous rents may 
^ten be seen in rocks which appear to have been 
9knply bndcen, the separated parts remaining 
in the same places ; but we often find a fissure^ 
several inches or yards wide, intervening between 
(he disunited pc^ons. These fissures are usually 
filled' ^th fine earth and sand, or with angular 
fragments of stone, evidently derived from the 
firacture of the contiguous rocks. 

The face of each wall of the fissure is often 
beautifully polished, as if glazed, striated, or 
fcored with parallel furrows and ri^es, such as 



*woiAd. lie pcoduced by iJne cantinaed jmbUng 
together of sur&ces of unequal hardness. These 
polished sur&ces are called by miners ^^ slicken- 
sid^." It is supposed that the lines of the striflp 
indicate the direction in which the rocks wer0 
moved* During one of the late minor earthquakes 
in Chili) the brick walls of a building were rent 
verticaUy in several places, and made to vibrale 
fox several minutes during each slK)ck» after which 
they remained uninjured, and without any open- 
ing, although the line of each crack was still visibla* 
When all movemeutr-bad ceased, there were seei^ 
on the floor of the house, at the bottom of each 
rent, small heaps of fine brickdust, evidently pro- 
duced by trituration. 

JFmUts. — It is not uncommon to find the mass 
of rock, on one side of a fissure, thrown up 
above or down below the mass with which it was 
once in contact on the other side. This mode, of 
displacement is called a shift, slip, or fault. ^'Tbe 
miner," says Play&ir, describing a faulty " is 
often perplexed, in his subterraneous journey, 
by a ;derangement in the strata, which change^ 
at once all those lines and be^ings which, h^d 
hitherto directed his course. When his. jn^iiie 
reaches a certain plane, which is som^tiip^es: peiv 
pendicular, as in A B, Fig. 76.,. sometimes obUque 
to the Jborizon (a^ in C D, ibi4•»)^he^ndB.th^ toods 
of arock broken asunder, those on the;6ne«ide of 



J>p 



rjjjvrB, 



tPiutt. 



J 


K 


Fig. •7^- 
c 




• 




\ 






^ 






\ 






• 


\== 




• •«•«•«•■■•■••>••« 



B D 

FandU. A B perpendicular, C D oblique to the karixon. 

the plane having changed their place, by sliding 
in a particular direction along the face of the 
others. In this motion they have sometimes prer- 
feerved their parallelism, as in Fig. 76., so that the 
strata on each side of the faults A B, C D, con- 
tinue parallel to one another ; in other cases, the 
strata on each side are inclined, as in a, £, c, dj 
(Fig. 77.), though their identity is still to be re- 




I^F^faitUorJUtureJUUdvrilhrMbbitktOneaehsfdeitfnkiehtketk^fUd 

ttrata are not paraUeL 

cognized by their possessing the same thickness, 
and the same internal characters.** * 

We sometimes see exact counterparts of these 
slips, on a small scale, in pits of fine loose sand and 
gravel, many of which have doubtless been caused 
by the drying and shrinking of argillaceous and 

• Playfair, Illust. of Hutt. Theory, J 42, 



eb,Y.} 



JFAU^TSf 



119 



f>ther becis, ^liglit 6Ul>sidf n^s^ haim^g t^m pi9C? 
from failyxi^ of sppp(»*t Soiiiietimesy howf^eri 
^ye^ diese small dips may have hew produced 
during ^earthquakes ; for Is^d has been moved^ .and 
its level, relatively to the sea» considerably ^Itered^ 
within the period when much of the aJOlavial sand 
and gravel now covering the sur&oe of contiawtl 
was deposited. 

I have already stated thc^t a geologist must be 
on his guard, in a region of disturbed strata^ against 
inferring repeated alternations of rocks, when, in 
fact, the same strata, once continuous, have been 
bent round so as to recur in the same section| 
and with the same dip. A similar mist^e has 
often been occasioned by a series of faults. 

15 for example, the dark line A H (Fig. 78.) 
represent the sur&ce of a country on which the 
strata ah c frequently crop o^t, an obs^erver, who 
is proceeding from H to A, might at first imaging 
that at every step he was approaching jiew stri^taf 



Fig. 78 




ApparefU aiternatwm of strata caused by vertical fauUa. 



120 Muiisrai Ipirti: 

>nrheredg the i^pefitbA of ifae- suBie' twds ^itf 
been cafised by y«tical fiwllBy or dowBtibfd^^ 
Thus, suppose the origiiiel jDass, A, B, Ct, B, td 
bave be^i a set of unifinrmly mdmed stHita, atid 
that the. different masses under E P, F JGr, and 
G D, sank down successively, so as to leave vacant 
the spaces marked m the dii^ram by dotted linei^' 
and to occupy those mark^ by tbe confinuous 
fainter lines, then let denudation take place 
along the line AH, so that the protruding and 
triangular masses indicated by the fiiinter lines 
are swept away, — a min^, who has not discovered 
the &ults, finding the mass a, which we will sup-" 
pose to be a bed of coal four times repeated^ 
might hope to find four beds, workable to an in-^ 
definite depth, but on arriving at the fault G he 
is stopped suddenly in his workings, upon reaching 
the strata of sandstone c, or on arriving at the line 
bf fault F he comes partly upon the diale h, and 
partly on the sandstone c, and on readung £ he 
is again stopped by a wall composed of the rock cL 
The very different levels at which the separated 
parts of the same strata are found on the different 
sides of the fissure, in some faults, is truly astonish- 
ing. One of the most celebrated in England is 
that called the " ninety-ffi^om dike," in the coal- 
field of Newcastle. This name has been given to 
it, because the same beds are ninety fathoms lower 
on the northern than they are on the southern side. 



Oi. Y.1 OBOOVSD MAFJUaetf OF FAULTS. 1^1 

Tbe fifln*e tet beisn fffled by a Wy of sand, 
^dttdk^ir-BMr' m Ae^ state of sandstone, and is 
cdlof ifte dOte^' ivMch k sometimes rery narrow, 
Imtia odiirpiaoes mom' Aan t^^enty yards wide.""^ 
The walk of the fissure are cfeored by grooves, snch 
as woidd bare been produced if the broken ends 
of the rock had been rubbed along the plane of 
the£Kiilt.f Inthe lynedaleand Craven fiiults, in 
the north of Ei^land, die vertical displacement is 
still greater, and the horizontal extent of the move- 
ident is from twenty to forty miles. Some geo- 
logists consider it necessary to imagine that the 
Inward or downward movement in these cases 
wa& acconoiplished at a single stroke, and not by 
a series of suddtni but intarupted movements. 
This idea appears to have been derived from a 
notion that the grooved walls have merely been 
rubbed in one direction. But this is so &r from 
being a constant phenomenon in faults, that it has 
often been objected to the received theory respect- 
ing dickensides, that the striae are not always 
parallel^ but often curved and irregular. It has, 
moreover, been remarked, that not only the walls 
of the fissare <Mr fault^butits earthy contents, some-* 
times present the same polished and striated faces. 
Now these &cts seem to indicate jpartial change^ 

* Godyhetart. and Phillips, Outlines, Stti p. 376. 
f Phil%% GwAogy, laxdi^t^jt Cyclop p. 41. 



123 OKIOIK OP fOPuiV 

in the direction of the moveineni, ami eamt 
alidiiigs subsequent to the first filling up of die 
fissure. Suppose the mass of rook A, B, C, ito^ 
overlie an exten^iFi^ chasm €f ^ fcnrmed at the depdi 

iSg. 79. 
A -« C 




of several miles, whether by the gradual contraetaon 
in bulk of a mass of strati^ baked by a mfxleraile 
heat, or by the subtraction of matter hy vdkaotue 
action, or any other cause. Now» if this region be 
convulsed by earthquakes, the Sa^vaseafp, and 
others at right aiigles to them, may sevcer the mass 
P from A and from C, so that i| may moveireeljs^ 
and begin to sink into the ch«3m. A fracture may 
be conceived so dean and perfi^t as to allov It to 
subside at once to the bottom of the fubterranean 
cavity ; but it is &x more probably that the sinking 
will be eiFected at successive periods during (Af- 
ferent earthquakes, the mass always eontibuii^ to 
slide in the same direction along the planes of the 
fissures/y, and the edges of the fidling «Aas8 being 
continually more broken and tritiin^ied at each 
convulsion. If, as is not improbably the cirdun- 
stances which liave caused the fiulure of support 
continue in operation^ at mny hajipsn ibat when 
the mass B l^a^ tinted Ae cavi^ first formed, its 



auYJ OBEAT 7AULT& |39 

foundations vnH again give way under it^ so that 
it will fall again in the same direction. But, if 
the direction should changei the &ct could not be 
discovered by observing the slickensides, because 
the last scoring would efface the lines of previous 
friction. In tiie present state of our ignorance of 
lEhe causes of subsidence, an bypothesis which can 
explain tiie great amount of displacement in some 
£iultS9 on sound mechanical principles, by a suc- 
cession of movem^its, is &r preferable* to any 
theory whicb assumes eacb &ult to have been ao- 
complisbed by a single upcast or downthrow of 
several thousand feet. For we know that there 
are operations now in progress, at great depths 
in the interior of the earth, by which both large 
and small tracts of ground are made to rise above 
and sink below their former level, some slowly 
and insensibly, otiiers silddenly and by starts, 
a few feet or yards at a time; whereas there are 
no grounds £>r believing that, during the last 3000 
years at least, any regions have been either up- 
heaved or depressed, at a single stroke, to the 
amount of several hundred, much less several 
thousand feet* 



6 2 



124 



CHAPTER VI. 

DENUDATION, AND THB PRODUCTION OF ALLUYIUIC. .^ 

X)enudation defined — Its amount equal to the entire' mass 
of stratified deposits in the earth's crust — Horizontal 
sandstone denuded in Ross-«hire -** Levelled sur&ce of 

r 

countries in which great fiiults occur — Connexion of 
denudation and alluvial formations — Alluvium, how dls« 
tingui^hed from rocks in situ — Ancient alluviums Called 
diluvium — Origin of these — Erratic blocks and accom* 
panying gravel-* Theory of their transportation by ice. 

Before we take leave of the aqueous or fossili- 
ferous rocks, we have still to consider the alluyial 
formadons. Denudation^ which has been occasionally 
spoken of in the preceding chapters, is the removal 
of mineral matter by running water, whether by 
a river or marine current, and the consequent 
laying bare of some inferior rock. Geologists are, 
perhaps, seldom in the habit of reflecting that this 
operation is the inseparable accompaniment of the 
production of all new strata of mechanical origin. 
The transport of sediment and pebbles, to form a 
new deposit, necessarily implies that there has 
been, somewhere else, a grinding down of rock into 
rounded fragments, sand, or mud, equal in 
quantity to the new strata. The gain at on6 
point has merely been sufficient to balance the 
loss at some other. A ravine, perhaps, has been 



Ch.VL] DENUDATION OF ROCKS. 125 

excavated, or a valley deepened, or the bed of the 
sea has, by successive upheaval, been exposed to 
the power of the waves, so that part of the su- 
perior txicvering of the earth's crust ha9 - been 
stripped off, and thus rocks, previously hidden, 
hav^,been^denuded. 

' \¥l3en we* see a stone buildings we know that 
somewhere, &r or near, a quarry has beenT>pened. 
The courses of stone in the biiilding may be com- 
pared to successive strata, the quarry to a ravine 
or valley which has' suffered denudation. As the 
strata, like the courses of hewn sfone, have been 
laid one upon another gradually, so the excavation 
both of the valley and quarry have been gradual* 
To pursue the comparison still farther, the super- 
ficial heaps of miid, sand, and ^lUvel usually c iUed 
alluvium, may be likened to the rubbish of a quarry 
which has been rejected as useless by the workmen, 
or has fallen upon the road between the quarry 
and the building, so as to lie scattered at random 
over the ground. 

If, then, the entire mass of stratified deposits in 
the earth's crust is at once the monument and mea- 
sure of the denudation which has taken place, on 
how sti^pendous a scale ought we to find the signs 
of this removal of transported materials in past 
ages ! Accordingly, there are different classes of 
phenomena^ which attest in a most striking man- 
ner the vast spaces left vacant by the erosive power 

G 3 




126 DENUDATION [Xhitl 

of water. I may allude first, to those Talleys on 
both aides of which the some strata, are seen felr 
lowing each other in the same order, and having 
the same mineral composition and fi)ssil contents. 
We may observe for example,, several formations, 
as Nos. 1, 2, 3, 4, in the accompanying diagram 
fig. 80, ^ (Fig* 80*); No;. 1. coi^lo- 

merate, Na2. day. No* 3b 
grit, and No. 4. limestone, 
each repeated in a series 

r<auyt €f d^nMkmT '^ ^ ^"U* Separated by vat 
a-aUuTiunk j^yg varyii^ in depth* 

When we examine the subordinate parts of these 
four formations, we find, in like manner, distinct 
beds in each, correspcmding, on the opposite sides 
of the valleys, both in composition and order of 
position* No one can doubt that the strata were 
originally continuous, and that some cause has 
swept away the portions which once connected the 
whole series. A torrent on the side of a mountain 
produces similar interruptions, and when we make 
artificial cuts in lowering roads, we expose^ in like 
manner, corresponding beds on either side. But 
in nature, these appearances occur in mountains 
several diousand feet high, and separated by iiH 
tervals of many miles or leagues in extent^ of 
which a grand exemplification is described by Dr* 
MacCulloch^ on the nortb-^westem coac^ of Bosa* 
shire, in Scotland* 

* Western Islands, vol. ii. p. 89. pi. 31. fig. 4. 



.auYZ2 OF STfAATtFVBD 1IOCK& 12^ 







^f red sandtiiMe <m nortk-mat oaast ^BatM-Mrt, 

The fimdamexital rock of that country is gneiss, in 
distur|>ed strata, on which beds of nearly horU 
soatal red sandstone rest imc(»ifomiably. The 
latter are dEiten very thin, forming mere flags, with 
their surface distinctly ripjde-marked. They end 
abruptly on the declivities of many insulated 
mountains, which rise up at once to the height of 
about 2000 feet above the gneiss of the surrounding 
plain or table-land, and to an average elevation of 
about 3000 feet above the sea, which all their 
summits generally attain. The base of gneiss 
varies in height, so that the lower portions of the 
sandstone occupy different levels, and the thickness 
of the mass is various, sometimes exceeding 3000 
feet. It is impossible to compare these scattered 
portions without imagining that the whole country 
has once been covered with a great body of sand* 
stone, and that masses from 1000 to more than 
3000 feet in thickness have been removed. 

But perhaps the most convincing evidence of 
denudation on a magnificent scale is derived from 
the levelled sur&ce of many districts in which 
large faults occur. I have already shown, in 
Fig. 78, p. 1 1 ^, and in Fig. 82, how angular and pro- 

o 4 






immm^'wum: 



C>)utnv 



tpyfiiag ^aaise^ of rock-zuigiit natorallj hs^e been 
looked for on the smrface immediately above gretM 
fiittltSy' althougk in fact dbey rarely e£sL lliis 
pj^^nom^non may be well studied in those districtis 
wher^ coal lias been extensively worked, for diere 
tbe fiina^ rela^tion of the beds whidi.faave fiiiifted 
tb^iir portion, may be determined with 'greet 'ax> 
Qurax^y.. .Thus in the eoal field of Ashby de la, 
Zquch^ in Leicestershire (see Fig. 82.), a fault oo- 

Kg. 82. 



rr 

I! 



!i * ll 



r 




AniAt and demukd coat strata, AMy de la Zaueh. 

curs, on one side of which the coal beds abed 
rise to the height of 500 feet above the corre- 
sponding beds on the other side. But the uplifted 
strata do not stand up 500 feet above the 
general sur&ce; on the contrary, the outline of 
the country, as expressed by the line z z^ is uni- 
form and unbroken, and the mass indicated by 
the dotted outline must have been washed away.* 
There are proofs of this kind in some level coun- 
tries, where dense ma£$!5es of strata have been 



See Mammat's Geological Facts, &c., p. 90. and plate. 



cshrvip DsuninMKi j^ 



dfaciedia^ajr'&aiik' areas «etmd himd^ed^ 

,., iXx the Newcastle ccxd district, it w asoertoinedf 
thatx&ultft obcur in which the upward or dowii-i 
wami inby^nent could not hare been less than 
140 &thonis, which, had thej affected equally the 
eonfigispation of the sur&ce to that amount, would 
produce nM>untains with precipitous escarpments 
near 1000 feet high, or chasms of the hk^ depth; 
yet .is the actual level of the country absolutely 
uniferm, a£Pording no trace whatever of subterra- 
neous disturbance.* 

The groimd from which these materials have 
been removed, is usually overspread with heaps of 
sand and gravel, formed out of the ruins of the 
very rpcks which have disappeared. Thus, in the 
districts above alluded to, rounded and angular 
fragments occur of hard sandstone, limestone, and 
ironstone, with a small quantity of the more de* 
structible shale, and even rounded pieces of coal, 
the form of these relics' pointing to water as the 
denuding agent. 

In geological descriptions we often read of " al* . 
luvium ^ and " diluvium," as opposed to " regular 
strata," or " fixed rocks," or " rocks in situ." It 
will be useful, therefore, to exphdn these terms^ 
At the surface there is commonly a layer of vege- 

• Conybeare*s Report to Brit. Assoc. 1832.j^.3aijiv * 

G 5 



190 ALLumriL Ci^vti. 

table monldy demed partly from decayed plants, 
and partly caused by the castings of earth-wOTmsy 
which are continually siftii^ the fine from the 
coarse soil.* Immediately beneath this mould 
the regular or fundamental stratified or imstrati* 
fied rocks of the district may appear ; but ther^ 
usually intervenes, if not an alluvial mass, at least 
a quantity of broken and angular fragments of 
the subjacent rock, provincially called rubble^ or 
brtzshy in many parts of England. This last may be 
referred partly to the weathering or disintegra- 
tion of stone on the spot, the effects of air and 
water, sun and frost, and chemical decomposition, 
and partly to the expanding force of the roots of 
trees, which may have grown in small crevices, 
at former geological periods, though they may 
now be wanting. Sometimes the vibrations and 
undulations of earthquakes may have had power, 
at some former era^ to shatter a surface previously 
rent and weathered. Thus in Calabria^ subter- 
ranean movements have been known to throw up 
into the air the slabs of a stone pavement f; and 
Mr. Darwin mentions, that in the Island of Qui- 
nquina, in Chili, scnne narrow riches of hard 
primary slate, which is there the fundamental 
rock, were as completely shivered by the vibrations 

* See Darwin on Formation of Mould, Proceedings of 
Geo). Soc. No. 52. p. 574. 
t See Princ of Geo!., Index, •< Calabria." 



of ^e great earthquake of February 1835, as if 

they had been blasted by gunpowder. The eff^t 

was merely superficialt and had caused fresh frao- 

tures and displacement of the soil, the slate below 

remaining solid and uninjured** 

Alluvium differs front the rubble or brash, just 
described, as being o<»nposed of sand and gravel, 
mmre or less rolled, in part local, but oflten in great 
part formed of materials transported from a dis- 
tance. The term is derived from alluvion an in- 
undation, or alluoj to wash. The gravel is rarely 
consolidated, often unstratified, like heaps of rub- 
bish shot from a cart, but occasionally divided into 
wavy and oblique layers, marking successive de>r 
position from water. Such alluvium is strewed 
alike over inclined and horizontal strata, and 
unstratified rocks ; is most abundant in valleys, but 
also occurs in high platforms, and even on lofty 
mountains, that of the higher grounds usually 
differing from that found at lower levels. 

The inferior surface of an alluvial deposit is 
often very irregular, conforming to all fhe in"* 
equalities of the subjacent rocL (Fig. 83.) Oc- 
casionatly a small massj as at c, appears detached, 
and as if included in the subjacent formation« 
Such isolated portions are usually sections of 
winding subterranean hollows filled up with al<< 

* Darwin^ p. 370. (for title see Bote, p. 137.) 

G 6 



^m\ 



KEuaiasfcm AXJLzrrioic 



{Jh^l* 




Figi as. luviiun. They may have 

been the courses ; of 
sprii^ or subterranean 
streamletS) which have 
flowed throu^ and ea-^ 
larged natural r^ats; or> 
when on a small scale, 

c.''maJ*^'S^appu«nt^ detached, whidi the roots of large 
trees have once occupied, gravel and sand having 
been introduced after their decay. 

It is not so easy as may at first appear to draw 
a clear line of distmction between the ^ed rocks, 
or regular strata, (rocks in situ^ or in place)y and 
their alluvial covering of travelled materials. If 
the bed of a torrent or river be dried up, we call 
the gravel, sand, and mud, left in their channels, or 
whatever, during floods, they may have scattered 
over the neighbouring plaiins, alluvium. The very 
same materials carried into a lake or sea, where 
they become sorted by water, and arranged in 
more distinct layers, are turned regular strata. 

In the same manner we may contrast the gravel, 
sand, and broken shells, strewed along the path 
of a marine current, with strata formed by the 
discharge of similar materials, year after year, into 
a deeper and more tranquil part of the sea. 

If any fossils occur, the mass may stil^ be called 
alluvial, provided the fossils appear to have been 



ch. vi.a TO jKMamhAM I aimATA. ■ tgtgi 



drifted td the fl{k>tl ; If any of them, as, for example, 
fireshwatec or marine shells,, seem ,to .bave lired 
and died where they are entombed, then the de- 
posit^ thou^ mainly consisting of drift materials^ 
should not be terined alluvial, but a regular marine 
or freshwater formation. It is, however, easy to 
perceive that passages must occur fix>m such, islr 
lavial to r^ular . dqxwits, both in the sea and the 
estuaries of rivers ; and it is Q&egi mcM difficult to 
distinguish between them, because organic remains 
have been often obliterated in formaticms of porous 
sand, gravel, and loam, which allow rainwater to 
percolate freely through them. 

After what has been said of the connexicm of 
denudation and alluvium, the student will expect 
to find alluviums of various ages, and at all heights 
above the sea, formed both before and during the 
emergence of ^land, but always most copiously at 
periods when the level of a country has undergone 
changes by subterranean movements; for then the 
course of running water, whether marine or fluviatile, 
has been most frequently deranged, and the power 
of the waves of the ocean has been broi^t to 
bear with the greatest effect against the land. * 

Before the doctrine of the rising and sinMhgof 
large continental areas, whether insensibly or by 
a repetition of sudden sjiocks, was admitted as 
part of the actual course of nature, all ancient 
alhiviums were classed by some authors, under the 



134 Avcnarr Axxmnum vtgtti. 

WBomon title of ^^diluvkun/' and were said not to 
be due to existing causes. To establish dus pro* 
position, it was thought sufficient to demonstmte 
that the nrers which may now hi^pen to drain 
a given district^ oould nerer^ in the course of 
thousands of ages, hare given rise to die valleys of 
denudation in which they now flow, and that these 
same rivers could never have washed into their 
present situations (often the summits of hills, and 
high table-lands,) all the gravdl and boulders evi- 
dently connected with former denuding operations. 
It was therefore usual to refer the ^ diluvium" to 
a deluge, or succession of deluges^ which rolled with 
tremendous violence over the land, after it had 
acquired its present configuration, and its present 
height above the sea. Not only small gravel, but 
large blocks of stone, were supposed to have been 
transported from a distance by these devastating 
floods or waves^ and lodged upon the hill-tops. 

But rivers, as we have seen, are not the only 
existing causes, nor even die most energetic agentSy 
by which denudation may be effected. If the 
upward movement of land be very slow, the waves 
may easily dear away a stratum of yielding ma- 
terials as fi»t as they rise^ and before diey reach 
dne surface. Thus^ a wide uninterrupted ex- 
panse of denudation may take plaoe^ and mnflsofi, 
many hundreds di feet or yards in thiftkupawj joay 
waste away by inches in the course of thousands 



CII.VI.] CAIJJBD DfLDTIOIi. IgJ 

€{ centories* But if ree& composed of a more 
Te&actory 8t<Hie dlionld at length rise u|v the 
lMieaker% as they foam over them, may still tear off 
fragments, and roll them along mitil the bottom of 
the sea becomes strewed orer with blocks and 
pebbles. This aUuvhan of marine origin will be 
^lifted when the ree& are ultimately converted 
into land, and may then constitute the covering 
of the suQimits of hills, or of elevated terraces, or 
table-lands* At the same time, this gravel may 
be wanting in all valleys excavated either during 
die rise of the land, by currents of the sea running 
between islands, or eaten out or deepened by 
rivers after the emergence of the land. At the 
bottom of such more modem valleys a distinct 
alluvium will be found, containing, p^haps, some 
pebbles washed out of the older or upland gravel, 
bat prmcipdly composed of the ruins of rocks le. 
moved during the erosion of the newer valleys. 

It must be remembered, that when we introduce 
flich an hypothesis, and take for granted the 
rise of the land out of the sea^ we are merely sup^ 
posing what we know, from the discovery of 
marine fossils, to have happened again and again* 
at former periods* 

Erratic blocks. — The great size of the boulders 
sometiiifees found associated with ancient alluviums, 
in places between which and the parent rock deep 
valleys) and even seas, now inierv^ie, has been 



thai]^hjb by gppie to oflfer .iii 8 ttn^ 
to as^ llieQiy vbich di^. not, intro^uee <;«iisiQ§f..Q{;. 
great yiol^icfe to accovntfor their reipoy^ Tbei^. 
Mocks^iCall^ erratic^ are some of l^m a few feet,^- 
others several yards» . in . diameter* They, ar^ • 
strewed by myriads over tiie sandy .comUrios :of 
the north of Germany, and parts. of Sweden, Ikoi?. 
mark, Finland, and Russia. Some of them at, 
least, must have been carried into their presteojt 
position, since the commencement of a very mod^n 
geological period, for they resl^ near StockhoUn» 
apd elsewhere, on layers of sand andjnarl cantainT 
ing shells of the species: now inhabiting the. Baltic 

Although these erratics are far more numerous 
in northern countries, some are met with as far 
south as the Swiss Jura, having evid^itly been 
carried thither from the Alps, a ehain which isr 
now separated from the Jura by one of the broadest 
and'deepest valleys in the w<»rld. 

Now it is inconceivable how any velocity of 
water could convey some of these huge masses, 
over seas and valleys, to the places where lliey 
are nmr found ; but there is no real, difficulty in 
su^ppsihg them to have been carried by ice» when 
th^ lands over whidi they lie scatta*ed were 3ub-* 
merged beneath the sea. 

As the reader may perhaps be incredulous re- 
specting the adequacy of the cause here alluded, 
to, I shall enuin£a:dte> Qiany feqts iseoently brought • 



cii.i«<ii jjfkxtteb tr ICE. jft^' 

I6^^t,.t¥faiek ineORtestably proVe h<ywiinpo^6ait 
a part ice plays in the transfer of alluyimn frmh 
place to place) and especially. of that containing 
large masses .of rock. I must confine raysd^ 
however, to a Imef deficription of a few examples, 
as it IS not the object of the present work to treat 
at lai^ of the changes illustrative of geological 
phenomena, npw known to be in progress on the 
earth. > 

First, in regard to the distribution of erratics; 
they occur, both in the northern and southern 
hemispheres, between the fortieth parallels of lati- 
tude and the poles, but are not met with in the 
intermediate equatorial and warmer regions.* 
This fact at once raises a presumption that the 
greater warmth of parts of Asia, Africa, and 
America, nearer the line^ has proved, unfavourable 
tx> the transport of such blocks. On the other hand, 
diey abound in the colder regions of North America, 
from. Canada northwards, as well as in northern 
Europe; and when we travel southwards, and cross 
• the Line in South America, we fall in with them 
again in Chili and Patagonia, between lat 41^ S. 
and Cape Hom.f Here, then, we have grounds 
for suspecting that a cold climate is favourable to 
the production of erratics. 

- ■ • . r w 4 

y ' ' ■ 

* See Mr. Darwin on some supposed exceptions to this 
general rule. Journal of Travels in South America, &c., 
1632 10 1836, in Voyage of H. M,S. Beagle, p. 289. 

-f Darwin, ibid. 



138 EBRATIC BLOCKS CPartl 

Now^ it is wdi knowiv tha^ anmniHy, ia the 
Beltie, stones are moved by ice; and, rery reoendy^ 
081 die shores of die Golf <^ Finland, some large 
firagments ^^re ascertained to have been carried 
to some distanee. in spring, when date fringe of 
ice which has endrcled die coi^t of die Gulf of 
Bodmia, and many parts of Sweden, Norway, and 
Denmark, during winter, breaks up, large stoneS) 
widi small gravel and ice, which have been firinly 
frozen into a soMd mass on die beach, are floated 
off to a distance. In Canada similar operations, 
but cm a grander scale, have been nodced by 
Captain Bayfield. In the river St Lawrence, die 
loose ice accumulates on the sboals during winter, 
at which season die water is low. The separate 
fragments of ice are readily frozen together in a 
dimate where the temperature is sometimes 90^ 
below zero, and boulders become entangled widi 
diem, so that in die spring, when die river rises, <m 
the melting of die snow, die packs are floated off, 
frequendy conveying away die boulders to great 
distances. A single block of granite, 15 feet long, 
by 10 feet bodi in widdi and height, and which 
could not contain less than 1500 cubic feet of 
stone, was in diis way moved down die river 
several hundred yards, during die late survey 
in 1837. Heavy anchors of ships, lying on the 
shore have in like manner been closed in and re- 
moved. In October, 1836, wooden stakes were 
driven several feet into die ground, at one point 



Ch. YLJ SBIFTBD BY ICI. |S( 

on the banks of tbe Sc lAwrence, at high water 
mark, and Cfver them were piled maaj boulden, 
as large as the united force of ok men could roIL 
The year after, all the boulders had disappeared, 
and otheiB had arriyed, and the stakes had been 
drawn out and carried away by the ice. 

It has also been observed, that ice-islands, de- 
tached &r to the north, perhaps in Baffin's Bay, 
are brought by the current, in great numbers, down 
the coast of Labrador every year, and are often 
carried through the straits of Belle Isle, between 
NewfouncBand and the continent of America, 
which, after passing through the straits, some- 
times float for several hundred miks t& the south- 
west, up the Gulf of St. Lawrence^ between the 
40th and 5(hh degrees of N. latitude. In one of 
these icebergs, hei^ of boulders, gravel, and 
stones were seen. 

A similar agency of ice extends in the southern 
hemisphere to still lower latitudes. Thus, for 
example, we learn from Mr. Darwin, that glaciers 
reaching down to the sea, occur at the head of all 
the sounds along the western coast of the southerly 
extremity of South America, in latitudes as low 
as 46^ and still farther, the ice being covered with 
great fragments of rock. Although these glaciers 
come down to the sea, the mountains from which 
they descend have 'only half the altitude of the 
Alps, and yet are equidistant from the equaton 
Portions of this South American ice, charged with 



140 ERRATIC BLOCKS. CFftrt i 

large blocks of granite^ were seen in Sir Geoige 
Eyre's sound, in the same parallel of latitude as 
Paris, floating outwards to the ocean.* 
. It is therefore natural to suppose that masses 
of rock may frequently be.carried by icebergs from 
the foot of the Andes, in this quarter of South 
America, across deep channels, and stranded on 
adjacent islands in the Pacific, such as Chiloe^ 
on which large erratics from the Andes are actually 
seen; and a general elevation of the mainland, 
together with the islands, accompanied by the lay- 
ing dry of the intervening sounds, might present 
to a future geologist a problem respecting the 
transport of blocks, as enigmatical as any which 
are now encountered in Europe, f 

Icebergs then, detached from glaciers together 
with coast ice, may convey, for hundreds of miles, 
pebbles, boulders, sand, and mud, and let these 
&11 wherever they may chance to melt, on sub- 
marine hills and valleys. These, wh^i the land 
emerges from the deep^ may constitute some of the 
&r-transported alluvium which has been ascribed 
to diluvial agency, j: 

a 
< .. 4 , . 

• Darwin, p. 283. (for tide, see p. 137.) 

t Darwin, ibid. p. 286. 

f For speculations on the causes of a local and goocnil 
change of climate, dependent on fluctuations in physical 
geography, and proofs of the wide conversion of sea into 
land in Earope, at periods companitiYcly nodem^ see Princ. 
of GeoL book L 



141 

• I I 



CHAPTER Vll. 

TOLCANIC ROCKS. - 

Trap rocks -- Name, whence derived <— Their igneous origm 
at first doubted •— Their general appearance and cha- 
racter — Volcanic cones and craters, how formed — 
Mineral composition and texture of volcanic rocks—? 
Varieties of felspar— Hornblende and au^te — Isomor- 
pfaism — Rocks, how to be studied— Basalt, greenstone, 
trachyte, porphyry, scoria, amygdaloid, lava, tuff — Alpha- 

. betical list, and explanation of names and synonyms, of 
volcanic rocks — Table of the analyses of minerals most 
abundant in the volcanic and hypogene rocks.' 

The aqueous or fossiljjferous rocks haying now 
been described, we have next to examine those 
which may be called volcanic, in the most extended 
sense of that term. Suppose a a in the annexed 

Fig. 84. 



5 




a* Hypogene formations,- stndfied and tinstradiied. 
h. Aqueous formations. c. Volcanic rocks. 

diagram, to represent the crystalline fondations, 
such as the granitic and metamorj^iic, b h thh 
fossiliferbus strata, and' c c the volcanic rocks. 
These last dre soinetim^ found, ^ was .explaitied 
iii the first chapter, and; Frontisi^eGe^ brealdtfg 



142 GENERAL AFFEARAKCE {Ttstil, 

thrcmgh a and &, sometimes overlyiiig both, and 
occasionally alternating with the strata b h. Thej 
also are seen, in some instances, to pass insensibly 
into the unstratiiSed division of c^ or the Platonic 
rocks. 

When geologists first began to examine atten- 
tively the structure of the northern and western 
parts of Eorope, they were almost entirely igno- 
rant of Ae phenomena of eidsting volcanos. 
They found certain rocks, for jthe most part with^ 
OBt stratification, and of a peculiar mineral com- 
position, to whidb they gave different names, such 
as basalt, greenstone, porphyry, and amygdaloid. 
All these, which were recognized as belonging to 
one family, were called " trap" by Bergmann 
(from trappay Swedish, for a flight of steps) —a 
name since adopted very generally into the nomen- 
clature of the science; for it was observed that 
many rocks of this class occurred in great tabular 
masses of unequal extent, so as to form a succes- 
sion of terraces, or steps, on the sides of hills. 
This configuration appears to be derived from two 
causes, &rst, the abrupt original terminations of 
sheets of melted matter, which have spread, whether 
(m the land or 'bottom of &e sea, over a le?et surfiioe. 
For we know, in the case of lava flowing fr«Mn*« 
volcano, that a stream, when it has ceased to fkfw^ 
and grown solid, very commonly ends in a steep 
i^ope, as at a, Fig. 86. But, secondly, the step-like 




appesranee arises mora 
ftequcntly from the mode 
JQ which honsontal wMM;y»s 
of igneous rock, such as 
6 Cy iotovwlated betireeA 
aqueous strata, hare, sob* 
sequentty to their origin, been eaqiosed, at diiC* 
lbra[it heights, by denudation. Such an outline, it 
is true, is not peculiar to trap rocks ; great beds of 
limestone, and other Jiard kinds of stone^ often pr^ 
senting similar terraces and precipices; but thesa 
are usnally on ^a smaller scaler or less numerous 
than the volcanic stq^s^ or form less decided fear 
tures in the landscape, as being less distinct in 
structore and composition from the associated 
rocks. 

Although the characters of trap rocks are 
greatly diversified, the beginner will easily learn 
to distinguish them as a class fix>m the aqueous 
fi3nnations« Sometimes they present themselves, 
as already stated, in tabular masses, which are not 
divided into strata, sometimes in shi^peless lun^ps 
and irregukur cones, forming small chains of hills. 
Often they are seen in dikes or wall-like masses^ 
intersecting fossiliferous beds. The rock is occa» 
sionally found divided into columns, often decom- 
posing into balls of various sises, from a few inches, 
to several feet tin diamet^. The dec<Hnposing. 
smrfiice very commonly assumes a coating of a^ 



144 TQUiAMtC BOODl zfmi.' 

muty inn eolour^ finna llie oxidation of ferragi*" 
nous matter, so ribmidanr. in the traps m lAick 
mapte (mt homblende occur ; or, in the fiebpathie 
narietiea of tn^ it aoquireB a iriiite opaque coat- 
Bg, firom the bleaching of the mineral called feW 
spar, (hi examining any of these volcanic rocks, 
where they have not suffered disint^ration, we^ 
rarely fiul to detect a crystalline arrangement in 
one or more of the component minerals. Sdme^ 
times the texture of the mass id odlular or porous, 
or has been porous, and llie cells hav« beeicnne 
filled with carbonate of lime, or other infiltrated 
mineral, which has thus taken the globular fi>nn 
of the cells. 

Most of the volcanic rocks produce a fictile scmI 
by their disintegration. It seems that their com- 
ponent ingredients, silica, alumina, lime, potash, 
iron, and the rest, are in proportions well fitted 
for vegetation. As they do not effisrvesce with 
acids, a deficiency of calcareous matter might at 
first have been apprehended; but although car<« 
bonate of lime is rare, except in the nodules of 
amygdaloids, yet it will be seen that lime some- 
times enters largely into the composition of angite 
and hornblende. (See Table, p. 166.) 

In regions where the eruption of volcanic mat- 
ter has taken place in the open air, and where the 
sur&ce has never since been subjected to great 
aqueous denudation, cones and craters are strik- 



flip, JHt 1 COHEI'. AKD ' CHAIVRS. ] 35 

iit^- chavaotanrtiK. Many hahdreds of diese 
tmm aie seen in central Frence, in l)ie ancient 
l^ovincec of Aurergne, Vejay, and Virar^s, where 
di^y obaerv^ for the most part, a Htiear srrange- 
meDtf and fi«m.cJiaiiiB of Inlls. Although none of 

Vig.86. 




(Bmope.) 

the eruptions have happened within the historical 
era, the streams of lava may still be traced dis- 
tinctly descending from many of the craters, and 
following the lowest levels of the existing valleys. 
The origin of the cone and crater-shaped hill is 
well underBtood, the growth of many having been 
watched during volcanic eruptions. A chasm or 
fisstu^ first opiens in the earth, ffom which great 
volumes of steam and other gases are evolved. 
"nie explosions are so violent as to hurl up into 
the air fragments of broken stone, parts of wliich 
are shivered into minute atoms. At the same 
time melted stone or lava usually ascends through 
the chimney or vent by which the gases make 
their escape. Although extremely ' heavy, this 
lava ia forced up by the expansive power of en- 
tangled gueaos fluids, chi^y steam ot aqueoui 



146 CONES AND CRATEBS. t^Utl* 

Tapour, exactly in the same manner as water is 
made to boil over the edge of a vessel when steam 
has been generated at the bottom by heat« Large 
quantities of the lava are also shot up into the air, 
where it separates into fragments, and acquires a 
spongy texture by the sudden enlargement of the 
included gases, and thus forms scoria^ other por- 
tions being reduced to an impalpable powder or 
dust. The showering down of the various ejected 
materials round the orifice of eruption, gives rise 
to a conical mound, in which the successive en- 
velopes of sand and scoriae form layers, dipping on 
all sides from a central axis. In the mean time a 
hollow, called a crater^ has been kept open in the 
middle of the mound by the continued passage 
upwards of steam and odier gaseous fluids. The 
kiva sometimes flows over the edge of the crater, 
and thus thickens and strengthens the sides of the 
cone ; but sometimes it breaks it down on one side, 
and often it flows out from a fissure at the base of 
thehiU. (See Fig- 86.) 

I have given a full history toid description of 
the phencmiena of recent volcanos in the Principles 
of Geology, and cannot repeat them here, but shall 
merely consider the characters of the igneous rocks 
as they appear to a geologist in the earth's crust. 
The subject may be treated of in the following 
order; first, the mineral composition, internal 
jtexture, and nomenclature of volcanic rocks; 



Cb. VIL] VOLCANIC BOCK& 147 

secondly) the loaxuier and position in whidi ibej 
occur in the earth's crusty and their external 
&nn8 ; and lastly, the conn^on between the pro« 
ducts of modem vqlcanos and the rocks usually 
styled trappean. 

Mineral composition cmd texture. -^ First, in re- 
gard to the composition of volcanic rodos, the 
varieties most frequently spoken oi^ are basalt, 
greenstone, syenitic greenstone, clinkstone, clay<» 
stone, and trachyte; while those founded chiefly on 
peculiarities of texture, are porphyry, amygdaloid, 
lava, tuff, scoriae, and pumice. It may be stated 
generally, that all these are mainly composed of 
two minerals, or families of simple minerals,^&par 
and hornblende^ some almost entirely of hornblende, 
others of felspar. 

These two minerals may be regarded as two 
groups, rather than species. Felspar, for example, 
may be, first, common felspar, that is to say, pot* 
ash-felspar, in which the alkali is potash {see 
Table, p. 166.) ; or, secondly, albite, that is to 
say, soda-Mspar, where the alkali is soda instead of 
potash ; or, thirdly, Labrador-*felspar (Labrador- 
ite), which differs not only in its iridescent hues, 
but also in its angle of fracture or cleavage, and 
its composition. We also read much of two oth^ 
kinds, called glassy felspar and compact felspar, 
which, however, cannot rank as varieties of equal 
importance, for both the albitic and common iel«- 

H 2 



146 YdLCAMIC MINERALS. IFitT. 

spar appear sometimes in transparent or glassjf 
crystals; and as to compact felspar, it is probably 
a compound of a less definite nature, sometimes 
Containing, according to Dr« MacCuUodh, both 
soda and potash. 

- The other group, or hornblende^ consists prin- 
cipally of two varieties ; first, hornblende, and, se- 
condly, augite, Mdiich were once regarded as very 
distinct, althoii^h now some eminent mineralogists 
are in doubt whether they are not one and the 
same mineral, differing only as one crystalline 
form of native sulphur differs from another* 

The history of the changes of opinion, on this 
point is curious and instructive, Werner first 
distmguished augite fi*om hornblende; and his 
proposal to separate them obtained afterwards the 
sanction of Haiiy, Mohs, and other celebrated 
mineralogists. It was agreed that the form of the 
crystals of the two species were different, and their 
structure, as shown by clea/vage^ that is to say, by 
breaking or cleaving the mineral with a chisel, or 
a blow of the hammer, in the direction in which 
it yields most readily. It was also found by ana- 
lysis that augite usually contained more lime, less 
alumina, and no fluoric acid; which last, thou^ 
hot always found in hornblende, often enters into 
its composition, in minute quantity. In addition 
to these characters, it was remarked as a geological 
&ct, that augite and hornblende are very raisely 
associated together in the same rock; and that 



Ch.yiU HORNBLENDi: AND AU0ITE. 14^ 

when this happened, as in some, lavas of moderq 
date, the hornblende occurs in the mass of the 
rock, -where crystallizadon may have taken place 
more slowly, while the augite merely lines cavities 
where the crystals may have been produced rapidly. 
It was also remarked, that in the crystalline slags 
of furnaces, augitic forms were frequent, the horn- 
blendic entirely absent^ hence it was conjectured 
that hornblende niight be the result of slow, and 
augite of rapid cooling. This view waa con* 
firmed by the &ct, that Mitscherlich and Berthier 
were able to make augite artificially, but could 
never succeed in forming hornblende. Lastly, 
Gustavus Rose fused a mass of hornblende in a 
porcelain furnace, and found that it did not, on 
cooling, assume its previous shape, but invariably 
took that of augite* The same mineralogtst obr 
served certam crystals in rocks from Siberia which 
presented a hornblende deavaffe^ whUe they had 
the external form of augite. 

If, from these data, it is inferred that the same 
substance Vnay assume the crystalline forms of 
hornblende or augite indifferently, according to 
the more or less rapid cooling of the melted mass, 
it is nevertheless certain that the variety com^ 
monly called augite, and recognized by a peculiar 
crystalline form, has usually more lime in it, and 
less alucaina, than that called hornblende, although 
the quantities of these elements do not seem to b^ 

H 3 



150 VOLCANIC MIMERALa tTtait 

always the same. Unquestionably the facts and 
experiments above mentioned show the very near 
affinity df hornblende and augite ; but even the 
convertibility of one into the other by melting 
and recrystallizing, does not perhaps demonstrate 
their absolute identity. For there is often some 
portion of the materials in a crjrstal which are not 
in perfect chemical combination with the rest. 
Carbonate of lime, for example, sometimes carries 
with it a considerable quantity of silex into its 
own form of crystal, the silex being mechanically 
mixed as sand, and yejt not preventing the car* 
bonate of lime from assuming the form proper to 
it. This is an extreme case, but in many others 
some one or more of the ingredients in a crystal 
may be excluded from perfect chemical union ; and 
after fusion, when the mass recrystallizes, the same 
elements may combine perfectly or in new pro* 
portions, and thus a new mineral may be produced. 
Or some one of the gaseous elements of the atnio» 
sphere, the oxygen for example, may, when the 
melted matter reconsolidates, combine widi some 
one of the component elements. 

The different quantity of the impurities or re- 
fuse above alluded to, which may occur in all but the 
most transparent and perfect crystals, may pardy 
explain the discordant results at which experienced 
chemists have' arrived in their analysis of the same 
mineral. For the reader will find that a mineral 



Ch. VIIJ THEORT OF I80H0RPHUM. |5| 

determined to be th^ same by its physical cha« 
facters, crystalliiie form, and optical properties^ 
has often been declared by skilful analysers to 
be composed of distinct elements. ( See the Table 
at p. 166.) Tliis disagreement seemed at first sub* 
▼ersive of the doctrine, that there is a fixed and 
Constant relation between the crystalline form and 
structure of a mineral, and its chemical composi« 
tion. The apparent anomaly, however, which 
threatened to throw the whole science of miners* 
logy into confusion, was in a great degree recon* 
died to fixed principles by the discoveries of Pro- 
fessor Mitscherlidh at Berlin, who ascertained that 
the composition of the minerals which had ap» 
peared so variable, was governed by a general 
law, to which he gave the name of isomorphism 
(firom t(ros, isos, equal, and /x^opfi}, morphe^ form). 
According to this law, the ingredients of a given 
species of mineral are not absolutely fixed as to 
their kind and quality; but one ingredient may be 
replaced by an equivalent portion of some ana* 
logons ingredient. Thus, in augite, the lime may 
be in part replaced by portions of protoxide of 
iron, or of manganese, nHiiile the form of the crys*- 
tal, and the angle of its cleavage planes, remain 
the same. These vicarious substitutions, however, 
of particular elements cannot exceed certain de- 
fined limits. 
Having been led into this digression on the rer 

H 4 



153 ^^^ ^ro DISTINGUISH ROCKS. llTwiiU 

cent progress of inm»al(^» I may here observe 
that the geological studsntmost endeavour as sooa 
as possible to &iniliarize himself with the-charac^ 
ters of five at least of the most abimdant simple 
minerals of which rocks are composed. These 
are, felspar, quartz, mica, hornblende and carbo^ 
nate of lime* This knowledge cannot be acquired 
from books, but requires personal inspection, and 
the aid of a teacher. It is well to accustom the 
eye to know the appearance of rocks under the 
lens. To learn to distinguish felspar from quartz 
is the most important stqp to be first aimed at; 
when these occur in a granular and uncrystallized 
state, the young geologist must not be discouraged 
if, after considerable practice, he oflen fails to disn 
tinguish them by the eye alone. If the felspar i& 
in crystals, it is easily recognized by its cleavage; 
but when in grains the blow-pipe must be used, 
for the edges of the grains can be rounded in the 
flame, whereas those of quartz are infusible. If 
the geologist is desirous of distinguishing the three 
varieties of felspar above enumerated, or horn-» 
blende fi*om augite, it will often be necessary to 
use the reflecting goniometer as a test of the angle 
of cleavage, and shape of the crystal. The use of 
this instrument wiU not be found difficult. 

The external characters and composition of the 
felspars are extremely different fi*om those of aur 
gite or hornblende; so that the volcanic rocks in 



QI-VIL3 BASALT* 153 

-Wbicb either of these minerals decidedly predo- 
minate «re easily recognized. But there are 
msct^ites of the two dements in every possible 
{HrQpc«tion». tbe mass being sometimes exclusively 
ctwposed of felspar^ at other times solely of 
migit^ Oi:, agalns of both in equal quantities. Oo 
cfiaionally, the two extremes, and all the interme- 
diate gradations, may be detected in one continuous 
inass., IJ^evertheless there are certain varieties or 
compounds which prevail so largely in nature, an(i 
preserve so much uniformity of aspect and com- 
position,, that it is useful in geology to regard them 
3s distinct rocks, and to assign names to them, 
such, as basalt, greenstone, trachyte, and others, 
already mentioned. 

Basalt. — As an example of rocks in which au- 
gite greatly prevails, basalt may first be mentioned. 
Although we are more familiar with this term 
than with that of any other kind of trap, it is difr 
ficult to define it, the name having been usee) 
sa vaguely. It has been very generally applied to 
any trap rock of a black, bluish, or leaden-grey 
colour^i having a uniform and compact texture. 
Most strictly, it consists of an intimate mixture of 
augite, felspar, and iron, to which a mineral of an 
olive green colour, called olivine, is often super- 
addec^ in distinct grains or nodular masses^ The 
ironia usually magnetic, and is often accompanied 
by another metal, titanium. Augite is the predor 

H 6 



154 GREENSTONE.. TRACHYTE. . tPwt I* 

minaut mineral, the felspar being in much smaller 
proportions. There is no doubt that many of the 
fine-grained and dark-coloured trap rocks, called 
basalt, contain hornblende in the place of augite ; 
but this ^mH be deemed of small importance after 
the remarks above made. Other minerals are oo- 
casionally found in basalt ; and this rock may pass 
insensibly into almost any variety of trap, espe- 
cially into greenstone, clinkstone, and wack^, 
which will be presently described. 

Greenstone^ or Dblerite^ is usually defined as a 
granular rock, the constituent parts of which are 
hornblende and imperfectly crystallized felspar; 
the felspar being more abundant than in basalt^ 
and the grains or crystals of the two minerals 
more distinct firom each other. This name may 
also be applied when augite is substituted for 
hornblende (the dolerite of some authors), or when 
albite replaces common felspar, forming the rock 
sometimes called Andesite. 

Syeniiic greenMone, — The highly crystalline com* 
pounds of the same two minerals, felspar and 
hornblende, having a gramtiform texture, and with 
occasionally some quartz accompanying, may he 
called Syenitic greenstone, a rock which fi*equently 
passes into ordmary trap, and as firequently into 
granite. 

Trachyte.*^ A porphyritic rock of a whitish or 
•greybh colour, composed principally of glassy fel- 



Ch. VU.] rORPBIBT. — AHTODALOUX 156 

wpar, with raystals of the same, generally with flome 
liomU^ide and some titaniferous iron. In con^ 
position it is extxetaelj different &oin basalt, this 
beii^^ a felspathic, as tJw other is an augitic, rock. 
It has a peculiar rou^ feel, whence the name 
Tpay(ui, trackta, ron^ Some varieties of trachyte 
contain crystals of quartz. 

Porphyry is merely a certain form of rock, very 
charact^stic of the volcanic formations. When 
distinct crystals of one or more minerals are sca^ 
tered through an earthy or compact base, the 
rock is termed a porjAyry. (See Fig. 87.) Thus 
trachyte is porphyritic ; for in it, as in many mo- 
Kg. 87. dem lavas, there are 

crystals of felspar; but 
in some porphyries the 
crystals are of augit^ 
olivine, or other mw 
nerals. If the base be 
greenstone, basalt, or 
■ pitchstone,the rockmay 
" v^!^ ' " ^ denominated green- 

stone-porphyry, and so forth. 

Jna/ffdaloid. — This is also another form of ig- 
neous rock, admitting of every variety of composi- 
tion. It comprehends any rock in which round or 
ahnond-shaped nodules of some mineral, such as 
agate, calcedony, calcareous spar, or zeolite, are 




156 AmraDALom. ti^uti. 

scattered dirougb a base of wack6, basalt, greets 
^ne, oi other kind of trap. It derives its name 
&ota the Greek word gmygdaia^ an ahnond, The 
origin of this structure cannot be doubted, for ve 
in&y trace the process of its formatioa in modem 
kivfifi. Sortall pores cw cells are caused by bubbleq 
of steam and gas confined in the melted matter* 
.After or during consolidation these empty spaces 
are gradually filled up by matter separaUng frotq 
^le mass, or iniiltered by water permeatii^ the 
rock. As these bubbles have been stmietimes 
lengthened by the Sow of the lava before it finally 
cooled, the contents of such cavities have the form 
of abnonda. In some of the amygdaloidal traps of 
Scotland, where the nodules have decomposed, the 
emp^ cells are seen to have a glazed or vitreous 
coating, and in this respect exactly resemble sco- 
TiaceouB lavas, or the slags of furnaces. 

The annexed figure represents a fragment of 




stone taken from the upper part of a dheet of b»- 
f&ltic lava in Aurergne* One half is Bcoriaceooai 
the pores bein^ perfectly empCyj the other part is 
amjgdaldidal, the pores or cells beingxnostly filled 
up with carbonate of lime^ forming Mvfaite kemds. 

ScoruB and Pumice may next be mentioned as 
porous rocks, produced by the action of gases on 
materiab melted by volcanic heat. Scarue are 
usually of a reddish brown and black colour, and 
are the cinders and slags of basaltic or augitic 
lavas. Pumice is a light, spongy, fibrous substance, 
produced by the action of gases on traehytic and 
other lavas; the relation, however, of its origin to 
the composition of lava is not yet well understood. 
Von Buch says it does not occur where only Xa- 
jbrador-felspar is present. 

Lavcu — This term has a somewhat vague sig- 
nification, having been applied to all melted matter 
observed to flow in streams fi*om volcanic vents. 
When this matter consolidates in the open air, 
the upper part is usually scoriaceous, and the mass 
becomes more and more stony as we descend, or in 
proportion as it has consolidated more slowly and 
under greater pressure. At the bottom, however^ 
of a stream of lava, a small portion of scoriaceous 
rock very frequently occurs, formed by the first 
thin sheet of liquid matter, which often precedes 
»the main current, or by contact with water in or 
upon the damp soil. 



158 IiAVA.~>TBAP TI7FF. [Put I. 

The more compact Isras are often porpfayrilic, 
but even tbe sooriaceous part sometimes contains 
imperfect crystals, vriaxh have been dmved from 
some older rocksy in whidi the ciystals pre^esisted, 
bnt ware not melted, as being more infusible in 
didr nature. 

Although melted matter rising in a crater, and 
even that which entars rents cm the side of a 
crater, is called lava, yet this term belongs more 
propa^ly to that which has flowed either in the 
open air or on the bed of a lake or sea. Jf di^ 
same fluid has not reached the surfiskce, but has 
been merely injected into fissures below ground, 
it is called trap. 

•There is every variety of composition in lavas; 
some are trachy tic, as in the Peak of Teneriffe ; 
a great number are basaltic, as in Vesuvius and 
Auvergne ; others are Andesitic, as those of Chili; 
^some of the most modem in Vesuvius consist of 
green augite, and many of those of Etna of augite 
and Labrador-felspar.* 

Trap tuff, fxfkanic tuff, — Small angular frag- 
ments of the scoriae and pumice, above mentioned, 
and the dust of the same, produced by volcanic 
-^cplosaons, form the tuffii which abound in all 
r^ons of active volcanos, where showers of these 
materials, together with small pieces of other 

* G. Rose, Ann. des Mines, torn. 8. p. 3d. 



^h. VII.] VOLCAinc TUFR 159 

Tocks ejected from the crater, fiJl down upon the 
knd mr into the sea. Here they ofben become 
mingled with shells, and are stratifieoL Such tuflb 
are sometimes bound together by a calcareous 
cement, and form a cftone susceptible of a beau- 
tiful polish* But even when little or no lime is 
present, there is a great tendency in the materials 
of ordinary tufi to coh^e together! 

Besides the peculiarity of their composition, 
some tufPs, or volcanic griUj as they have been 
termed, diflfer from ordinary sandstones by the 
angularity of their grains. When the fragments 
are coarse, the rock is styled a volcanic Ireodeu 
Tufouxous conglomerates result frcxn the intermix- 
ture of rolled fragments or pebbles of volcanic 
and other rocks with tuff. 

According 'to Mr. Scrope, the Italian geolo- 
gists confine the term tuff^ or tufa, to felspathose 
mixtures, and those composed principally of 
pumice, using the term peperino for the basaltic 
tuffs.* 

We meet occasionally with extremely compact 
beds of volcanic materials, interstratified with 
fossiliferous rocks, much resembling the trap 
which may be found in a dike. These may some- 
times be tuffi, notwithstanding their density or 
compactness. The chocolate-coloured mud, which 

* Geol. Traas, vol. ii. p. Sll. Second Series. 



ISp YOLCAKIG ROCK& CFUill. 

was pojured for weeks out of the crater of Grar 
ham's Island, ii^ the Mediteixaiieaii> in 1831» must, 
wh^i unmixed with other materials, h^ve conr 
stituted a stone lieavier than granitew Each cubip 
inch of the impalpable powder which has fidlen 
for days through the atmosphere during some 
modem eruptions, has been found to weigh, with- 
out being compressed, as much as ordinary trap 
rocks, which are often identical in mineral com- 
position. 

The fusibility of the igneous rocks generally 
exceeds that of other rocks^ for there is muclji 
alkaline matter and lime in their composition, 
which serves as a flux to the large quantity of 
silica, which would be otherwise so refractory an 
ingredient. 

It is remarkable, that notwithstanding the abun- 
dance of this silica, quartz is wanting in the vol- 
canic rocks, or is present only as an occasional 
mineral, like mica. The elements of mica, as of 
quartz, occur in lava and trap, but the circum- 
stances under which these rocks are formed, are 
evidently im&vourable to the development of 
mioa and quartz, minerals so characteristic of the 
hypogeuQ fonu^ions« 

It would be tedious to enumerate all the 
varieties of trap and lava which have been re- 
garded by different observers as sufficiently abun- 
dant to • deserve distinct iiaiiies, especially as each 



iai.VII.] VOLCANIC BOCK& Ifff 

investigator is too apt to exaggerate the import* 
ance of local varieties which happen to prevail In 
districts best known to him. It will be useful, 
however, to subjoin here, in the form of a glos- 
sary, an alphabetical list of the names and sy- 
nonyms most commonly in use, with brief ex- 
planations, to which I have added a table of the 
analysis of the simple minerals most abundant in 
the volcanic and hypogene rocks. 



Explanation of the namesj synanymsy and mineral 
composition of the more abundant volcanic rocks* 

Amphxbolitk. See Hornblende rock| amphibole being Haiiy's 

name for hornblende* 
Amtgdalqip. a particular form of Yolcanic rock; see p. 155. 
Auom aocK. A kind of basalt or greenstone, composed wholly 

or principally of granular augite. {Le(mhard*t MmeraU 

reicht, 2d edition, p. 85.) 
AKTGiTic-roBPHTBT, Crystals of Xiabrador-felspar and of augite, 

in a green or dark grey base, ( Rose^ Anru des Minest tom* 8f 

p. 22. 18S5.) 

Basalt. Chiefly augite — an intimate mixture of augite and 
felspar with magnetic iron, olivine, &c. See p. 153. The 
yellowish green mineral called olivine, can easily be distin- 
guished from yellowish felspar by its infusibiUty, and having 
no cleavage. The edges turn brown in the flame of the 
blow-pipe. 

Clatsionx mod Ci^XRom^voBrflTBT. An earthy and compact 
stone, usually of • purplish colour, like an indurated .clay i 



162 MINERAL COMPOSITION tPatl. 

pawn into hornstone; geaerally contains scattered crystals 
ot felspar and sometimes of quarts. 

CuxxsTONi. S^ PhonoUte, fissile Fetrosilex; a greenish or 
grayisk rock, having a tendency to divide into slabs and 
columns; hard, with clean fracture, ringing under the 
hammer ; principally composed of compact felspar, and, ac- 
cording to Gmelin, of felspar and mesotype. (Leonhard, 
MmenUreiclUf p. 102.) A rock much resembling clinkstone, 
and called by some Petrosilez, contains a considerable per- 
centage of quarts and fekpar. As both trachyte and basalt 
pass into clinkstone, the rock so called must be very various 
in composition. 

Compact FxLsrAB, which has also been called PetrosUex ; the 
rock so called includes the hornstone of some mineralogists, 
is allied to clinkstone, but is harder, more compact, and 
translucent. It is a varying rock, of which the chemical 
composition is not well defined, and is perhaps the same as 
that of clay. (J/oe CuAocA's CUu$ykotion cf Uocks, p. 481.) 
Dr. MacCuUoch says, that it contains both potash and soda. 

CoaKXAK. A variety of claystone allied to hornstone. A fine 
homogeneous paste^ supposed to consist of an aggregate of 
felspar, quartz, and hornblende^ with occasionally epidote, 
and perhaps chlorite; it passes into compact felspar and 
hornstone. (De la Beche, Geok Trant, second series, vol. 2. 
p. S.) 

DiALLAGnaocc* S^n. Euphotide^ Gabbro, and some OphiolitM. 
Compounded of felspar, and diallage, sometimes with the 
addition of serpentine, or mica, or quartz. (JITocCu^cft, 
ibid, p. 648.) 

DiouTX. A kind of greenstone, which see. Components, 
felq>ar and hornblende in grains. According to Rom, Amu 
des Minei, tom. 8. p. 4., diorUe consists of albite and horn- 
blende. 

Bioamc-ToapRTar. A porphyrittc greenstone, composed of 
crystals of albite and homblendie, in a greenish or blackish 
base. (Rote, ibid, p. 10.) 

DoLxaiTX. Formerly defined as a synonym of greenstone, which 
■le. But according to Roae (ibid. p. as.}» ita conapovtion is 
black aogite and L«bndor4dapars aoeordii^ to Leonhard 



eh.yjij OF VOLCANIC ROCK& I63 

{MmeraheichSf &c. p. 77.)* a^gite, Labnidor-felt|NV, anl 
magnetic iron. 
DoMrrx. An earthy condition of trachyte, ibund in die Vuj Ait 
Dome, in Auvergne. 

EuTHOTiDX, A mixture of graiDs of Labrador-felspar and dial* 
lage. {Bose, ibid, p. 19.) According to some^ Hm rock 
is defined to be a mixture of augite or hornblende, and Sana- 
surite, a mineral allied to jade. {AUan*$ Mtnerahgy, p. 158.) 
&e Diallage rock. 

FELsrAR^roRPHTRT. St/Tu Homstone-porphyry ; a base of feU 
spar, with crystals of felspar, and crystals andgndns of quarta* 
See also Homstone. 

Gaxsro, see Diallage-rock. 

GsxxNSTOKx; Syn, Dolerite and diorite; components, horn- 
blende and felspar, or augite and felspar in grains. See 
above, p. 154. 

Grxtstonx, (Graustein of Werner.) Lead grey and greenish 
rock, composed of felspar and augite, the felspar being more 
than seventy-five per cent. (^Scrope, Jourtu of ScL No. 42. 
p. 221.) Greystone lavas are intermediate in compositiom 
between basaltic and trachytic lavas. 

HoRNBLXKDX ROCK. A gTcenstoue^ composed wholly or prin^ 
dpally of granular hornblende^ or augite. (Leonhard, Mi^ 
nertUreichs, &c., p. 85.) 

HoRKSTONx, HoRKSTOKK-poRrHTRr. A kind of felspar porphyry, 
{Le<mhardf ibid,) with a base of homstone, a mineral ap- 
proaching near to^ flint, differing irom compact felspar in 
bdng infusible. 

HTPXRsrHXNE ROCK, R mixture of grains of Labrador-felspar and 
hypersthene, {Rose, Ann, des Mines, tom. 8. p. 13.), having 
the structure of syenite or granite'; abundant among the 
traps of Sky. In a geological view, it has been called a green- 
stone, in which hypersthene takes the place of hornblende. 

MxtAPBTRx. A variety ot black porphyry, the base being black 
augite with crystals of felspar ; from /ucAof, melas, black. 



164 MINERAL COMPOSITION [Partly 

Obsidiak. "^treous lava like melted glass, nearly allied to 
pitchstone. 

OrHiotiTXf sometiines same as Diallage rock {Leonhard, p. 77*}^ 
sometixnes a kind of serpentine. 

Ophuz. a green porphyritic rock, composed chiefly of horn- 
blende, with crystals of tliat mineral in a base of the sam^ 
mlted with some felspar. It passes into serpentine by a 
tnixture of talc. (J&urat*5 D^Attbuissonf torn. 2. p. 63.) 

FzARLSTONx. A volcanic rock having the lustre of another of 
pearl ; usually having a nodular structure ; intimately related 
to obsidian, but less glassy. 

!l^£PJEaiKo. A form of volcanic tuff, composed of basaltic scoriae 
See^, 159. 

FzTaosiLxx. See Clinkstone and Compact Felspar. 

Fhonolite. St^, of Clinkstone, which see. 

FiTciisTOKE ; vitreous lava, less glassy than obsidian ; a blackish 
green rock resembling glass, having a resinous lustre and 
appearance of pitch ; composition various, usually felspar 
and augite; passes into basalt; occurs in veins, and itii 
Arran forms a dike thirty feet wide, cutting through isand- 
stone ; forms the outer walls of some basaltic dikes. 

PoBrHTKT.' Any rock in which detached crystals of felspar, or of 
one or more minerals, are ^diffused through a base.* See 
p. 155. 

FozzoLANA, A kind of tuff. See p. IS, 

FuMicz. A light, spongy, fibrous form of trachyte. See p. 157* 

FvaoxENic-PoapuTaT, same as augitic-porphyry, pyroxene bein^ 
Haiiy's name for augite. 

ScoBi^s. Sh/iu volcanic cinders; reddish brown or black po« 
jous form of lava. See p. 157. 

^x&pxNxiNX. A greenish rock, in which there is much magnesia ; 
4isually contains diallage, which is nearly allied to the simple 
mineral called serpentine. Occurs sometimes, though rarely, 
in dikes, altering the contiguous strata ; is indifferently a 
member of the trappean or hypogene series. 

$7XNXTZc-oauNSTONx; composition, crystals or grains of felspar 
and hornblende. See p. 154, 



OlVII.]*^ of volcanic ROCK& |0| 

TzFHBiNE, synonymous with lava. 

ToADSTONK. A local name in Derbyshire for a kind of wack^, 

which see. 
Tbachytk, chiefly composed of glassy felspar, with cfystals 

of glassy fekpar. See p. 154. 
Trap tuff. See p. 158. * 

T&Ass. A kind of tpff or mud poured out by lake-craters during 

eruptions ; common in the £ifel, in Germany* • 
Tdfacxous conolohxbatb. See p. 159. 
Tuff. jS^. Trap-tuif, volcanic tuff. See p. 158. 

Viritsoos KATA. See Pitcfastone and Obsidian. 
Volcanic toff. See p. 158. 

Wackk. a soft and earthy variety of trap, having an argilla- 
ceous aspect. It resembles indurated clay, and when 
scratched, exhibits a shining streak. 

Wbivstonf. a Scotch provincial term for greenstone and 
other hard trap rocks. 



ANALYSIS OF IIIIIBRAL& 



g a 
fcS 



1 pi! 


1 III:; : :s i 


1 i, l|l>5|?!8;;.ISss 


1 :ii: ::>;:::::: 




■81 
9S-I 




1 :Pisi::i;Mi 


s 


U:m%m:::: 




AlinnfiK. 

SO-53 
19-44 

80-17 

18-5 
179 

2-2 
Sl- 
17-02 
17-5 
18-94 
27-25 


i SSS5 'S ;. s. ss??. 


i SSS5S .SSSSS5SSSS9 


iliiuri ii 1 



ANALTSIS OF SflMERALS. 



1 6-^*' ^ B »>»■ 

1 2-6 i 1 ISiS 


ill; > ! !!■;•; 


f*si^ ;,.,Ji!i..s 


15-09 

1-75 
1-96 




a trace 
21-35 

11-08 

0-48 
0-71 




13-85 
1-S 
11- 

1-33 

0-28 
0.5 
2-89 




|"22; ■..=>■ .s-"sgsgs 












;:;::;::::f::!:i 

liiiilirirlip 

lIljIIMilllll^ 


' 



I 

U 

n 



168 



't 



CHAPTER Vin. 

• » • 

TOLCANic BOCKS — cotUmuetL 

Trap dikes -^ sometimes project — sometimes leave fissures 
vacant hj decomposition — Branches and veins of trap -* 
Dikes more cryttfJSine in the centre — ^Foreign fragments of 
rock imbedded — Strata altered at or near the contact — 
Obliteration of organic remains — Conversion of chalk 
mto marbte — and of coal into coke — Inequality in the 
modifying influence of dikes — Trap interposed between 
strata — Columnar and globular structure — Relation of 
trappean rocks to the products of active volcanos — Sub-> 
marine lava and ejected matter corresponds generally to 
ancient trap. 

Having in the last chapter spoken of the com- 
position and mineral characters of volcanic rocks, 
I shall next describe the manner and position in 
which they occur in the earth's crust, and their 
external forms. Now the leading varieties, such 
as basalt, greenstone, trachyte, porphyry, and the 
rest are found sometimes in dikes penetrating stra- 
tified and unstraUfied formations, sometimes in 
shapeless masses protruding through or overlying 
them, or. in horizontal sheets intercalated between 
strata. 

Volcanic dikes, — Fissures have already been 
spoken of as occurring in all kinds of rocks, some 
a few feet, others many yards in width, and often 



ChTflL] VOLCAinc DtXm l0f 

filled up with eunh m angular pieoea of atODe^ or 
with sattd and pebbles. Instead of such material^ 
ni{^x)se a quantity of melted stone to be dm«ii 
or injected into an open rent, and there consoli- 
dated, we have then a tabular mass resembling a 
wall, and called a trap dike. It is not uncommon 
to find such dikea passing through strata of soft 
loaterialB, audi as tuff or shal^ which, being more 
perishable tlian the trap, are often washed away 
by the sea, rivers, or rain, in which case the dike 
stands prominently out in the iace of precipices, 
or on the level surface of a country, (See the 
annexed figure.) * 

, Itg. 89k 




In the islands of Arran, Sky, and other parts 
of Scotland, where sandstone, conglomerate, and 
other hard rocks are traversed by dikes of trap^ 
the oonverBe of the above phenomenon is seen. 

' I liave been &voured vith thk dm^ng b; Captain 
^.HaU. 



170 



[Partt 




The dike having decomposed more rapidly than 
the containing rock, has once more left open the 
original fiesure, often ibr a distance of many yank 
Fig. 90. inland from the sea-coast^ 

as represented in the an- 
nexed view. (Fig. 90.) 
In these instances the 
greenstone of the dike 
is usually more tough 
and bard than the sand- 
stone; but chemical ac- 
tion, and chiefly the 
oxidation of the iron* 
ha* given rise to the 
more rapid decay. 
There is yet anothei- case, by no means uncom- 
mon in Arran and other parts of Scotland, where 
the strata in contact with the dike, and for a cer- 
tain distance from it, have heen hardened, so as 
to resist the action of the weather more than the 
dike itself, or the surrounding rocks. When this 
happens, two parallel walls of indurated strata are 
seen protruding ahove the general level of the 
country, and following the course of the dike. 

As fissures some times send offbranehes, or divide 
jnto two or more fissures of equal size, so also we 
find trap dikes biftircatang and ramifying, and 
sometimes they are so tortuous as to be called 
veins, though this is more common in granite than 



Cb, VIllJ 



TRAP-DIKBS AND VSma 



171 



Fig. 91. 




in trap. The accompanyuig sketch (F^.91.) by Dr* 

MacCulloch represents 
part of a. sea-diff in Ar« 
gyleshire,. where an over- 
lying mass of trap, by sends 
out some veins which ter« 
minate downwards. An- 
TnvvehuimMraumurthtm. Other trap Vein, a a, cuts 
through both the limestone, c, and the ti*ap, A, 
. In Fig. 92. a ground plan is given of a ramify- 
ing dike of greenstone, which I observed cutting 
through sandstone on the beach near Kildonan 
Castle, in Arran. The larger branch varies from 
five to seven feet in width, which will afford a 
scale of measurement for the whole. 




Ground plam<Vt greenttone dike traversiHg tandstone. Arran. 

In the Hebrides and other countries the same 
masses of trap which occupy the surface of the 
country far and wide, concealing the subjacent 

Fig. 93. 



^ M 




2W91 MMitgMd e99etiag umdttwt near StdsknMk At SSIy. (MacCuDoeh.) 

I 2 



^7i ^yjiiuvdv$ r^sM'^GP ' t^u€t 



Hratifi^^i^ock^ are seen alM iaiihe'flea^diffiy .{ttt^ 
loiiged' *<knnmard8 in Teins or dikes, "wbieh p«o«- 
bably unite with other masses of igneous rock at 
a greater depth* The largest of the dEkes r^e- 
saited in the annexed diagram, and which ait 
s6<^ in part of' the coast of Sky, is no less^ diam 
lOO feet in width* 

Every viariety of trap rock is sometimes found 
in these dikes, as basalt, greenstone, felspar<« 
porphyry, and more rarely trachyte. The amyg- 
daloidal trap§ also occur, and ev^i tuff and 
breccia, for the materials bf these last may be 
washed down into open fissures at the bottom of 
the sea, or during eruptions on the land may be 
showered into -them from the air. 

Some dikes of trap may be followed for leagues 
uninterruptedly in nearly a straight direction, as 
in the north of England, showing that the fissures 
which they fill inust have been of extraordinary 
length. 

IXkes more <^staUvne in the centre* ' — la many 
cases trap at the edges or sides c^ a dike is kss 
^crystalline or more earthy than in the centre, in 
tonsequence of the melted matter having <;oded 
more rapiiUy by coming in contact with die' cold 
sides' of liie fissure^ whereas, in the centre^ the 
'mktter of th^ dike being kept long im a fluid or 
ttifi state, the cry^uds are slowly formed. In the 
aneient part 'of Vesuvim a* dun btfnd of hal£mliE^ 
ous lava is found at the edge of some dikes* At 



,^m^'i 



TRAJr.]HK£B> ANI> VBIKSL 



m 



the jiytliStbii^r greenstone dikes with limostpae, ^ 
mUb€Kndi or fidinage^ of serpentine 19 oeeasion^Uj 
dbservecL . ' 

• On die left shore of the fiord of Christiaiiiai i)l 
Norway^ « remarkable dike of syenitio greenaton^ 
la taraoed tlu'ough transition strata, until at .lengthy 
in the promontory of Naesodden, it enters miea- 
sefaifit Fig« M. represents a ground plan^ where 

Fig. 94. 
SifenUie greemUme tUke qf N^noOdeUt Ckristiania. . . 




Green- S^eniUc rock. Green, 
stone, stone. 



the dike appears eight paces in width, In the 
zniddle it is highly crystalline and granitifomi) of 
a purplish colour, and containing a few crystals of 
mica, and strongly contrasted with the whitish mica- 
schist, between which and the syenitic rock there 
is usually on each side a distinct black band^ 18 
inches wide, of dark greenstone. When first seen, 
these bands have the appearance of two accompany- 
ing dikes; yet they are» in fact, only the difierent 
ferm which the syenitic materials havd assumed 
ipi^here near to or in contact with the micdrochlst* 
At one point, a, one of the sahlbands ter^^in^^ 



x3 



;':/«•. ^ 



174 7OKBI0N FXAaHBRTS IN DIKES. [nrtt. 

Sot a space ; but near this there is a large detached 
block by having a gneiss-like stmctore, consisting 
of hornblende and felspar, vhich is included in the 
midst of the dike. Round this a smaller aicircUng 
zone is seen, of dark basalt, or fine^;nuned green- 
stone> nearly corresponding to the larg^ ones 
which border the dike, but only <me inch wide.* 

The iact abore alluded to, of a fbrogn frag- 
ment, such OS b (Fig. 94.), included in the midst 
of the trap, as if torn off irom some subjacent 
rock or the walls of a fissure, is by no means 
imcommon. A fine illustration is seen in a dike 
of greenstone, ten feet wide, in the northern 
suburbs of Christiania, in Norway, of which the 
annexed figure is a ground plan. Hie dUce passes 




through shale, known by its fossils to belong to 
the transition, or Sihirian series. In the black 
base of greenstone are angular and roundish 
pieces of gneiss, some white, others of a light 

* This dike has been described by Professor Keilhau, of 
Chiiatiuua, in whose companj lesaauned it. 



ph. yill.]! ROCKS ALTERED BT DIKEa 175 

jlesh-colour, some without lamination, like granite, 
others with laminae, which, by their various and. 
often opposite directions, show that they have 
been scattered at random through the matrix^ 
These imbedded pieces of gneiss measure from 
one to about eight inches in diameter. 

Mocks aUered by volcanic dikes* — After these 
remarks on the. form and composition of dikes 
themselves, I shall describe the alterations which 
they sometimes produce in the rocks in contact 
With them. The changes are usually such as the 
intense heat of melted matter and the entangled 
gases might be expected to cause. 
. PlaS'Newydd. — A striking example, near Plas- 
Newydd, in Anglesea, has been described by 
Professor Henslow.* The dike is 134 feet wide^ 
Stnd consists of'^a rock which is a compoxmd of 
felspar and augite (dolerite of some authors).. 
Strata of shale and argillaceous limestone, througK 
Tfhich it cuts perpendicularly, are altered to a 
distance of thirty, or even, in some places, to 
thirty-five feet from the edge of the dike. The 
shale, as it approaches the trap, becomes gradually 
more compact, and is most indurated where 
nearest the junction. Here it loses part of its 
Qchistose structure, but the separation into paral- 
lel layers is still discernible. In several places 

^ Canlbridge Transactions, vol. i. p. 402.. 

I 4 



jii|f|^«( /rIgt-tiie-jBost hardened i)Bi1^;6f49ie:ln^ 
^eloflpil:. ^ImOIS) principally JProduda^ P^ mmlf 
obHl»r4M»e4> yet eren here ^it knpteBdLo&s ttiMiry 
firequ0iii(ly be tntoed; The argillaceoiul^ liio^Umcr 
^^rg!»€9 lOsakigous mutadons, losing its earthy 
ti^^ture ^^. it approachieg the ^Ske^ dnd becoming 
gsQOIullur . and oryBtalline* But the D^st ejctfa** 
ordinary . phenomenon is the appeatance in "^le 
shale; of numemus crystals of anaicinie and garliet^ 
whii^ apre .distinctly confined to those p<H'tidns of 
the' rock affected by the dike.* Garnets have 
been observed, under very analogous ciroem* 
i^ances, in High Teesdale, by Professor Sedgwick, 
wh^e.>they occur in shale and limestone^ altered 
by basalt f 
-jtnirint* — In several parts of the county of 
Antrim,, in the north of Ireland^ chalk with flints 
is traversed by basaltic dikes« The chalk is there 
coirrerted mto granular marble near the basalt, 
the A&nge sometimes extending eight or ten feet 
froBi the wall of the dike, being greatest near the 
point (^contact, and thence gi*adually decreasing 
titi it becomes evanescent. ** The extreme effect,** 
sajrs Dr. Berger, *« presents a dark browii (Crystal- 
line limestone, the crystals running in flakes as 
large ad those of coarse primitive {Tnetamorphic) 

* Cambridge Tmaaatdooa, toL u p. 410^ 
f Ibi4 fpLii. p. 175. 



jpk^Nii.] KCTur nan. )^f 

Umfietone; the Mxt state is HKxfamiie, thnk-fiMi 
graiaed a^ii wewiCBCHia ; a tiompsetTUiefy, ktnin^ 
apurvdiwMwa wp^t sods Uui§h>grey mioati 
s»«eeeda.: .this, bnruds the outer ' edge) IbeeiHn^ 
fc^m^vhit^ and inseaisibl; gtsduates hKo thie'' 
ifuaUered ch^k. The flints in the altered ehaUt 
OEoaUy assiune a grey yellowish eolourt"* All 
traces o{ <^|;amc remains are efibeed in that part 
(f the limestone which is most crystidline. 

' The annexed drawing (Fig. 96.) represents 
duree baasltic dikes traversing die chalk, all within 

Kg. 96. 




the distance of ninety feet The chalk coptigwws 
to the two outer dikes b converted into a findly grti' . 
nular marble, m tn, as are the whole of the jsasses 
between the outer dikes and the central, ooei The. 
entire contrast in the compoattioo and cc4our.of the 
intrusive and invaded rocks, in these cases, render^ 
the phenomena peculiarly clear and interesting. 
.Another of the dikes of the nerthret^t of Ire- 

• Dr. Be^er, Gtol. Tnnx., WoMt Series, vo). ul. p. ITS. 

t Geol. Trana., Fitat Series, voLiu, p.'eie. sad plate 10. 

1 5 



178 ftOCKS AVTEgEli \VaHt 

land has converted a mass of red tendstone into 
homstone.* By another, the slate clay of the ooal 
measures has been indurated, and has assumed 
the character of flinty slate f ; and in another place 
the slate clay of the lias has been changed into 
flin^ slate, which still retains numerous impre&* 

sions of ammonites. 4: 

* It might have been anticipated that beds of coal 
would, from their combustible nature, be affected 
in an extraordinary degree by the contact of 
melted rock. Accordingly, one of the greenstone 
dikes of Antrim, on passing through a bed of coal, 
reduces it to a cinder for the space of nine feet 
on each side. § 

At Cockfield Fell, in the north of England, a 
similar change is observed. Specimens taken at 
the distance of about thirty yards from the trap 
are not distinguishable fit>m ordinary pit coal; 
tiiose nearer the dike are like cinders, and have 
all the character of coke ; whil6 tiiose close to it 
are converted into a substance resembling soot. || 

As examples might be multiplied witiiout end, 
I shall merely select one or two otiiers, and then 
conclude. The rock of Stirling Castie is a cal- 

* Geol. Trans., First Series, vol. liL p. 201. 
t Ibid. p. 205. 

:|: Ibid. p. 213.; and Play&ir, Illust. of Hutt. Theory, 
8. 253. 

§ Ibid. p. 206. 

II Sedgwick, Camb. Trans. vol.ii. p. 37. 



Cb.Vni.: BY. TRAP DIKEflL \J^ 

careous sandstone^ fractured, and forcibly displaced 
by. a mass of greenstone, which has evidently in- 
vaded the strata in a melted state. The sandstone 
has been indurated^ and has assumed a texture 
approaching to homstone near the junction* I]\ 
Arthur's Seat and Salisbury Craig, near Edin* 
burgh, a sandstone which comes in contact with 
greenstone, is converted into a jaspideous rock, * • 
• The, secondary sandstones in Sky are converted 
into solid quartz in several places, where they 
^eome in contact with veins or masses of trap ; and 
abed of quartz, says Dr. MacCuUoch, found near a 
mass of trap, among the coal strata of Fife, was in 
all probability a stratum of ordinary sandstone^ 
having been subsequently indurated and turned 
into quartzite by the action of heatf 
' But although strata in the neighbourhood of 
dikes are thus altered in a variety of cases, shale 
being turned into flinty slate or jasper, limestone 
into crystalline marble, sandstone into quartz, coal 
into coke, and the fossil remains of all such strata 
wholly or in part obliterated, it is by no means 
uncommon to meet with the same rocks, even in 
the same districts, absolutely unchanged in the 
proximity of volcanic dikes. 

This great inequality in tlie e£Pects of the ig- 

♦ Blust. of Hutt. Theory, § 253. and 261. Dr. MacCul- 
loch, Geol. Trans., First Series, vol. ii. p. 305. 
, . + Syst. of GebL voLi* p.206. , - 

I 6 



heMli» to^ tttay bhen. arise from an original fliiP* ' 
feMi«^ ik tiieir' temperature, and in diat of th^ ' 
entarigled ga^^ such as is ascertained to prevail 
in- difiereiit lavas, or in die same lava near its 
sauTQe and at a distance from it« ' The power 
ald^'^of the invaded rocks to conduct heat itus^ 
vary, according to their composition, structure, and 
the-fraotures which they may have experienced, and 
perhaps, also, according to the quantity of water 
(so capable of being heated) winch they contain* 
It must happen in some cases that the component 
materials are mixed in such proportions as prepare 
them readily to enter into chemical union, and 
form new minerals; while in other cases the mass 
may be more homogeneous, or the proportions less 
adapted for such union. 

We must also take into consideration, that one 
iSssure may be simply filled with lava, which may 
begin to cool from the first; whereas in other cases 
the fissure may give passage to a current of melted 
matter, which may ascend &r days or months, 
feeding streams which are overflowing the country 
above^ or are ejected in the shape of scoriae firom 
some crater. If the walls of a rent, moreover, are 
heated by hot vapour before the lava rises, as we 
know may happen on the flanks of a volcano, the 
additional caloric supplied by the dike and its 
gases will act more powerfully. 

Intrusion of trap betwetnstraiiU'^In proof of the 



OnKUtJ FOB£IBI.T IMTBUDS) TBAF. 1^1(1 

mBfiita»cai force which the fluid tnf iuUaoauHi 
tiipes exerted on the rooks into whicih it ba& in- i 
tnided itself, I may refer to the Whin-Sill, where 
a mass of baBalt, £rom six^ to eighty feet iiii 
height, represented by <i. Fig. 97., ii. ^ pact- 
wedged in between the rocks of Emefltone* bt aod . 
shale, c, which have been separated from tbe.grewt 
mass of limeetoae and shal^ d, with which tbey^ 
e united. 




The shale in this place is indurated ; and the 
limestone, which at a distance from the trap is 
blue, and contains fossil corals, is here converted 
into granular marble without fossils. 

Masses of trap are not nnfrequently met with' 
intercalated between strata, and maintaining iheix 
parallelism to the planes of stratification through- 
out large areas. They must in some places have 
forced their way laterally between the divisions of 
the strata, a direction in which there would be 

■ Oamh.Tra«. ToLiL p.l80. 



J82 .'COLUMNAR SCRUCTUBE . ' tl'^^I* 

the least resistance to an advancing fluid, if no 
vertical rents communicated with the sur&ce, and 
a powerful hydrostatic pressure was caused by 
gases propelling the lava upwards. 

Columnar and ghbular structure. — One of the 
characteristic forms of volcanic rocks, especially 
of basalt, is the columnar, where large masses 
are divided into regular prisms, sometimes easily 
separable, but in other cases adhering firmly to* 
gedier. The columns vary in the number of angles, 
from three to twelve ; but they have most com- 
monly from five to seven sides. They are often 
divided transversely, at nearly equal distances, 
like the joints in a vertebral column, as in the 
Giants' Causeway, in Ireland. They vary exceed- 
ingly in respect to length and diameter. Dr. 
MacCuUoch mentions some in Sky which are about 
400 feet long; others, in Morven, not exceeding 
an inch. In regard to diameter, those of Ailsa 
measure nine feet, and those of Morven an inch or 
less.* They are usually straight, but sometimes 
curved ; and examples of both these occur in the 
island of Stai&. In a horizontal bed or sheet of 
trap the columns are vertical ; in a vertical dike 
they are horizontal. Among other examples ef the 
last-mentioned phenomenon is the mass of basalt, 
called the Chimney, in St. Helena (see Fig. 98.), 
a pile of hexagonal prisms, 64 feet high, evidently 

♦ Ma^CuUoch, Syst. of Geol. voLii. p. 137. 




Fig. 99. 



OF VOLCANIC KOCKS^ IgS 

the remunder of a narrow 
dike, the walls of rodt 
which the dike ongmally 
traversed having been re- 
moved down to the level 
of the sea. In Fig. 99. 
a small portion of this 
dike IS represented on a 
less reduced scale.* 

It being assumed that 
columnar trap has con- 
solidated from a fluid state, the 
I prisms are said to be always at 
1 right angles to the cooling sur^ 
m faces. If these surfaces, there- 
' fore, instead of being either 
perpendicular or horizontal, are 
curved, the columns ought to be inclined at every 
angle to the horizon ; and there is a beautiful 
exeiQplification of this phenomenon in one of the 
valleys of the Vivarais, a mountainous district in 
the South of France, where, in the midst of a 
r^ion of gneiss, a geologist encounters unex- 
pectedly several volcanic cones of loose sand and 
scoriae. From the crater of one of these cones, 
called La Coupe d'Ayzac, a stream of lava de- 
scends and occupies the bottom of a narrow val- 
ley, except at those points where the river Volant, 
* Seale'i Qeognoay of St. Helena, plate 6. 




op th^ torrents which join it, have cut awqi; {Mir- 
tipnB of the solid lava* The accompanying sketch 
(Fig« \0Q.) isepresents the renmiuit of the lava al^' 

F%, liDO. 




Ifav0 qf La Compe ^AsfKoe^ near Aniraigtte, in the Provbicc qf ArdMke. 

one c^ the points where a lateral torrent joins the 
main valley of the Volant It is clear that the 
lava once filled the whole valley up to .the dotted 
lineVa; but the river has gradually swept away 
all bdow that line, while the tributary torrent 
has laid open a transverse section ; by which we 
percdive, in the first place, that the lava is com- 
posed, as usual in this country, of three parts ; the 
uppermost, at a, being scoriaceous; the second, £, 
presenting irregular prisms ; and the third, c, widi 
regular ed^mns, which are vertical on the banks 
of the Volant, where they rest on a horizontal 
base of gneiss, but which are inclined at an togU ; 
of 45^ at^, aiid flien hmzontal at^ theli* positbit *. 
having been every where determined, according to 
the few before mentioned, by the con^ve fbrm'of 
the original vall^. 



or ioitivic ibcka 



1^' 




■ "bi Ae iuniexe<)'flgtire'(lOl.) a view is gi^'- 

a of some of the inclined 

J and carved columns 

I viach present tbemselves^ 

on the sides of the tbI- 

ileys in the hilly region 
north of Vicenza, > in 
Italy, and at the foot of 
the higher Alps.* Un- 
like those of the Vivarus, 
last mentioned, the ba- 
salt of this country was 
evidently submarine, and the present Talleys have 
since been hollowed out by denudation. 

The colunmar structure is by no means peculiar 
to the trap rocks in which hornblende or augite 
predominate; it is also obserred in clinkstone) 
trachyte, and other felqiathic rocks of the igneous 
cUss, although in these it is rarely exhibited in 
such regular polygonal forms. 

It has been already stated that basaltic ct^umns 
are often divided by cross joints. Sometimes 
each s^ment, instead of an angular, assumes a 
sp^roidal form, so that a pillar is made up (tf a 
pile of balls, usually flattened, as in ^ Chees»< 
grotto at Bertrich-Baden, in the Eifel, near the 



■ Fort^ VUm. sur I'Hist, NM. de I'ltalie, torn, i.' p. SSS,. 



189 COLDHMAS AND : IPutL 

Moselle. (Fig. 102.) The basalt, there, is part of 
Fig los 




a small stream of lava, from 30 to 40 feet thick, 
which has proceeded from one of several volcanic 
craters, still extant, on the neighbouring heights. 
The position of the lava bordering the river in 
this valley, might be represented by a section like 
that already given at (Fig. 100, p. 184.), if we 
merely suppose inclined strata of slate and the 
argillaceous sandstone called greywacke to be 
substituted for gneiss. 

In some masses of decomposing greenstone, 
basalt, and other trap rocks, the globular struc- 
ture is BO conspicuous that the rock has the ap- 
pearance of a heap of large cannon balls. 

A striking example of this structure occurs in 
s trachyte or pitchslone-porphyry jn one 



.Ch.VniJ QIOBULAX STKDCTUKE \QJ 

of &.e Ponza islands, which rise from the Medit^S- 
ranean, off the coast of Terracina aqd Gaiety 
The globes vary from a 
few inches to three feet 
in diameter, and are of 
an elhpsoidal form. (See 
Fig 103.) Thewholerock 
19 in a state of decomposi- 
tion, "and when the balls," 
( I says Mr. Scrope, " have 
I been exposed a short time 
1 to the weather, they scale 
^off at a touch into nu- 
I merous concentric coats, 
3 like those of a bulbous 
Low'^^hjijI'di '"'^^ inclosing a compact 
I. (Scrope.) nucleus. TQie laminae of 
lucleus have not been bo much loosened by 
decomposition; hut the application of a ruder 
blow will produce a still further exfoliation. * 

A firaile texture is occasionally assumed by 
clinkstone and other trap rocks, so that they have 
been used for roofing houses. Sometimes the pris^' 
matic and slaty structure is found in the same 
mass. The causes which give rise to such arrange^ 
ments are very obscure, but are supposed to be 
connected with changes of temperature during the 

* Scrope, Oeol. Tnaw. vol. iL p. 20S. Second Series. 




Moliqg of ihe maaS) as lyill be pomted aiit ia .the 
jiipigiid< (See Chap. X*) 

Relation of trappean rocks to the products ^f active 

volcanos. 

• When we reflect on the changes above described 
in the strata near their contact with trap dikes, 
and consider how great ]a the analogy in compo* 
sition and structure of the rocks called trappean 
and the lavas of active volcanos, it seems difficult 
at first to luiderstand how so much doubt could 
have prevailed for half a century as to whether 
tss^ was of igneous or aqueous origin. To a certain 
extent, however, there was a real distinction be« 
twiteti the trappean formations and those to which 
the term volcanic was almost exclusively confined* 
3%e trappean rocks first studied in the north of 
Germany, and in Norway, France, Scotland, and 
Other countries, were either such as had been 
formed entirely under deep water, or had been in-* 
jeeted into fissures and intruded between strata, 
ttnd which had never flowed out in the air, or over 
the bottom of a shallow sea. When these products, 
Aerefore, of submarine or subterranean igneous 
aetioa were contrasted with loose cones of scdrlse, 
tuff, and lava, o^ with narrow streams of lava in 
great? part scoriaceous and porous, such as were 
observed to have proceeded fix)m Vesuvius and 
EtiMi) liie resemblance seemed remote and i^ui- 



yooaL It iira% in trwtlv like c(»ipariiig the tOMs of 
a tree with its leaves and brsoiclies, whicii^ altboagli 
they belong to the same plant, differ in form, tei^ 
tote, colour, mode of growth, and position. The 
external cone, with its loose ashes and porous lava, 
inaj be likened to the light foliage and brandies, 
9fld the rocks concealed fiur bdow, to the roots* 
But it is not enough to say of the Toleano^ 

" quantum verdce in auras 
'' iEtherias, tantum radice in Tartara tendit," 

Ibr its roots do literally reach downwards to Tkm 
tarns, or to the regions of subterranean fire; and 
what is concealed fiur below, is probably always 
more important in volume and extent than wiiat 
is visible above ground. 

We have already stated how firequendy dense 
masses of strata have been removed by denudatioii 
from wide areas (see Chap. VI.) ; and this fiM 
prepares us to except a similar destruction of whatr^ 
ever may once have formed the uppermost pari 
of ancient submarine or subaerial Voloaaos, mover 
eq>ecially as those superficial parts lore always df 
the lightest and most perishable inatieffials» * Thf9 
abrupt manner in which dikes of trap usually t^« 
minate at the surface (seeFig»104.),iuidthe waJdiH 
worn pebbles of trap in the ajluvium whi^b cov^ink 
the dike, prove ineontestaUy that whfit^irer, wiiaf 
uppermost in these fonnations bfw. becAr sin^ 



loliirtii iv31 enM^ fisBDct tiie deep lA eaevfer'Ae 
botfeom of the sea beoomoi hud. * 

The propoirtion of Tcdcanic matter wbick is oxi* 
guiftUy wibiaariiie must always be very great» as 
those volcanic vents which Bxe not ^itlrely benealir 
the ^ea» sjte almost all of them in idands^ <»*, if on 
continents^ near the shore. This may explain why 
extended sheets of trap so often occur, instead of 
narrow threadsi like lava streams. For, a mukn 
tade of causes tend, near the land, to reduce the 
bottom of the sea to a nearly uniform level, — tbo 
sediment of rivers,— materials transported by the 
waves and currents of the sea from wasting clifi% 
-—showers of sand and scoriae ejected by volcanos, 
and scattered by the wind and waves. When, 
therefore, lava is poured out on such a surface, it 
will spread &r and wide in every direction in a 
liquid sheet, which may afterwards, when raised 
up, form the tabular capping of the land. 

As to the absence of porosity in the trappean 
formations, the appearances are in a great degree 
deceptive, for all amygdaloids are, as already ex* 
plained, porous rocks, into the cells of which mi- 
neral natter, such as silex, carbonate of lime^ and 
other ingredients, have been subsequently intnn 
duced. (See p. 156.) 
. In the little Cumbray, one of the Western 

• See Princ of GeoL, Index, ** Graham Island," « Kyoe," 
^ Copf^mciates, volcanic,* &c. 



Umdi» hms Anwi, llie amygdaloid sotnetkiMi 
tH>iitKiii8 elongated cairitieft ^ed "vrith lirown tpsar; 
•and when tke Hodtdes have been wadied out, the 
iaterkur of the cavities is gkaed with the Titreeius 
tarnish so charaeteristic of die pores of daggy 
lavas. Even in some parts of this rode whieh are 
exehided from air and water, the cells are empty^ 
and se^n to have always remained in this stat^ 
and are therefore nndistinguishable from some 
modem lavas.'' 

Dr. MacCulloch, after examining with great at- 
tention these and the other igneous rocks of Scot- 
land, observes, ^^ that it is a mere dispute about 
terms, to refuse to the ancient eruptions of trap 
the name of submarine volcanos; for tliey are such 
in every essential point, although they no longer 
eject fire and smoke." f The same author also 
considers it not improbable that some of the vol- 
canic rocks of the same country may have been 
poured out in the open air. | 

Although the principal component minerals of 
subaerial lavas are the same as those of intrusive 
trap, and both the columnar and globular struc- 
ture are common to both, there are, nevertheless, 
some volcanic rocks which never occur as lava, 
sucB as greenstone, clinkstone, the more crystal- 
line porphyries, and all those traps in which 

* MacCuUocb, West. Isl., vol. xi« p. 487. 

f Syst. of Geol., voLii, p, 114. % Ibid. 

K 



194 VOLCANIC ROCKa tnnL 

([juartz and mica frequently aj^ar as constituent 
parts. In short the intrusive trap rocks, forming 
the intermediate step between lava and the plu-^ 
tonic rocks, depart in their characters from lava 
in proportion as tdey approximate to grmiite. 

These views respecting the relations of the vol* 
canic and trap rocks will be better miderstood, 
when the reader has studied, in the next chapter, 
what is said of the plutohic formations. 



195 



CHAPTER IX. 

PLUTONltJ BdCKS — GRANITE. 

General aspect of granite — Decomposing into spherical 
masses — Kude columnar structure — Analogy and difier- 
ence of volcanic and plutonic formations — Minerals in 
granite, and their arrangement — Graphic and porphyritic 
granite — Occasional minerals — Syenite — Syenitic, lal- 
cose, and schorly granites — Eurite — Passage of granite 
into trap — Examples near Christiania and in Aberdeei^ 
shire — Analogy in composition of trachyte and granite— 
-Granite veins in Glen Tilt, Cornwall, the Yalorsinc, and 
other countries — Different composition of veins from 
main body of granite — Metalliferous veins in strata near 
their junction with granite-^ Apparent isolation of nodules 

• of granite — ij,uartz veins — Whether plutonic rocks are 
ever overlying — Their exposure at the surface due to 
denudation. 

The plutonic rocks may be treated oT next in 
order, as they are most nearly allied to the vol- 
canic class, already considered. I have described^ 
in the first chapter, these plutonic rocks as the 
unstratified division of the crystalline or hypo- 
gene formations, and have endeavoured to point 
out in the Frontispiece, at D, the position which 
they occupy, when first formed, relatively to the 
volcanic formations, B. 

By some writers, all the rocks hdW under con^ 
sideration have been comprehended under th6 

K 2 



m 



GENERAL ASPECT 



CPurt I. 



n^me of granite, which is, then, understood to em- 
brace a large femily of crystalline and compound 
rocks, usually found underlying all other form- 
ations; whereas we have seen that trap very 
commonly overlies strata of different ages. Gran- 
ite often preserves a very uniform character 
throughout a wide range of territory, forming 
hills of a peculiar rounded form, usually clad with 
a scanty vegetation. The surface of the rock is 
for the most part in a crumbling state, and the 
hills are often surmounted by piles of stones like 
the remains of a stratified mass, as in the annexed 
finrure, and sometimes like heaps of boulders, for 

Fig. 105. 




Mass qf granite near the Sharp Tor, ComwaU. 

which they have been mistaken. The exterior of 
these stones, originally quadrangular, acquires a 
rounded form by the action of air and water, for 
the edges and angles waste away more rapidly tlian 
the skies. A similar spherical structure has al- 
ready been described as characteristic of basalt, 
axul other volcanic formations, and it must be 
referred to analogous causes^ as yet but imperr 
fiacdy 'Understood. 



Ch.IXO OP OHAKITE. IQ? 

Although It is die general peculiarity of granite 
to assume no definite shapes, it Is nevertheless 
occasionally subdivided by fissures, so as to assutne 
a cuboidal, and even a columnar, structure. Ex- 
amples of these appearances liiay be seen near the 
Land's End, in Cornwall, (see figure.) 

Fig. 106. 




The plutonic formations also agree with the 
volcanic, in having veins or ramifications proceed- 
ing from central masses into the adjoining rocks, 
and causing alterations in these last, which will 
be presently described They also resemble trap 
K 3 



199 WMDui, coHnMrnoN wti 

in conukung no organic renuuns; but they differ in 
being store uniftam in texture, whole mounts 
masses of indefinite extent appearing to have 
ori^nated under conditionB precisely aimilar. But 
they differ in never being woriaceoua (» amyg- 
daltHdal, in never forming a porphyry with aa 
^ncrystalline base, and never alternating with 
tuflfs. Nor do they ibrm conglomerates, although 
there la sometimes an insensible passage from a 
6ne to a coarse grained granite, and occasionally 
patches of a fine texture are imbedded in a 
coarser variety. 

Felspar, quartz, and mica are usually con- 
sidered as the minerBls essential to granite, the 
felspar being most abundant in quantity, and the 
proportjon of qaartx exceeding that of mica. 
These minerals are united in what is termed a 
confused crystallization ; that ia to say, there is no 
regular arrangement of the crystals in granite, as 
in gneiss (see Fig. 107.), except Iq the variety 
Pg.107. 




termed graphic granite, which occurs motttir ii 



ch. a.] OP eBAHinc bocu. 199 

granitic veins. This rariety is a compound of fel- 

spwr and quartz, so arranged as to produce an 

imperfect laminar structure. The crystals of fekpa^ 

Kg. 108, Fig. 109. 




appear to have been first formed, leaving between 
tbem the space now occupied by the darker coloured 
quartz. This mineral, when a section is made at 
right angles to the alternate plates of felspar and 
quartz, presents brdcen UneSj which have beeft 
compared to Hebrew charafiters. 

Porphyritic graaite. — This name has been 
sometimes given to that varie^ in which large 
crystals of felspari sometimes laoTe than an inch 
in length, are scatteTed through an ordinary base 
of granite. An example of this texture may be 
seen in the granite of the Land's End, in CoruT 
wall. (Fig. 1 10.) The two larger prismatic crystals 
in this drawing represent felspar, smaller crystals 
of which are also seen, similar in form, scattered 
through the base. In this base also appear black 
qtecks of mica, the oystals of which have a more 
K 4 



POBPH1R1TIC OBAHITK 

Fig. na 




Fcrrkt^ie gmiiiu, Laafi End, CorrHsaO. 

or less perfect hexagonal outline. The remainder 
of the mass is quartz, the translucency of which is 
strongly contrasted to the opaqueness of the white 
felspar and black mica. But neither this trans- 
parency of the quartz, nor the silvery lustre of the 
mica, can be expressed in the engraving. 

The uniform mineral character of large masses 
of granite seems to indicate that large quantities 
of the component elemenlB were thoroughly mixed 
up together, and then crystallized under precisely 
similar conditions. There are, however, many 
accidental, or " occasional, " minerals, as they are 
termed, which belong to granite. Among these 
black schorl or tourmaline, actinoUte, zircon, gar- 
net, and fluor spar, are not uncommon ; but they 
are too sparingly dispersed to modify the general 
aspect of the rock. They show, nevertheless, that 
the ingredients were not everywhere exactly the 
same ; and a still greater variation may be traced 
in tfie ever-varying proportions of the felspar, 
quartz, and mica. 



ClklX.] SYENITE-. TALCOSE ORAMITB. ^| 

Syenite. — When hornblende is the substitute 
for mica, which is very commonly the case, the 
rock becomes Syenite; so called from the cele^ 
brated ancient quarries of Syene in Egypt, It 
has i^the appearance of ordinary granite, except 
when miheralogically examined in hand specimens, 
and being fully entitled to rank as a geological 
member of the same plutonic &mily as granite. 
Syenite,' however, after maintaining the granitic 
character throughout extensive regions, is not 
uncommonly found to lose its quartz, and to pass 
insensibly into syenitic-greenstone, a rock of the 
trap family. 

Syenitio^ranite, — The quadruple compound of 
quartz, felspar, mica, and hornblende, may be so 
termed. This rock occurs in Scotland and in 
Guernsey. 

Talcose granite^ or Protogine of the French, is 
a mixture of felspar, quartz, and talc. It abounds 
in the Alps, and in some parts of Cornwall, pro- 
ducing by its decomposition the china clay, more 
than 12,000 tons of which are annually exported 
from that county for the potteries.* 

Schorl rock, and scborly granite. — The former 
of these is an aggregate of schorl, or tourmaline, 
and quartz* When felspar and mica are also 
present, it may be called schorly granite. This 
kind of granite is comparatively rare. 

* Boase on Primary Geologjr, p. 16. 



^02 PASSAGE OP Cl*«rtl. 

Eurite. — A rock in which all the ingredients 
of granite are blended into a finely granular mass. 
Crystals of quarts and mica are sometimes scat- 
tered through the base of Eurite. 

Pegmatite* — A name given by French writers 
to a variety of granite ; a granular mixture of 
quartz and felspar; frequent in granite veins; 
passes into graphic granite. 

All these granites pass into certain kinds of 
trap, a circumstance which affords one of many 
arguments in favour of what is now the prevailing 
opinion, that the granites are also of igneous 
origin. The contrast of the most crystalline form 
of granite, to that of the most common and earthy 
trap, is undoubtedly great; but each member of 
the volcanic class is capable of becoming por- 
phyritic, and the base of the porphyry may be 
more and more crystalline, until the mass passes 
to the kind of granite most nearly allied in mineral 
composition. 

The minerals which constitute alike the granitic 
and volcanic rocks, consist, almost exclusively, of 
seven elements, namely, silica, alumina, magnesia, 
lime, soda, potash, andiron; and these may some- 
times exist in about the same proportions in a 
porous lava, a compact trap, or a crystalline 
granite^ It may perhaps be found, on farther 
examination, for on this subject we have yet much 
to learn, that the presence of these elements in 
pertain proportions is inore favoiirable than in 



Ch. IX.} GRANITIS INTO TRAP. 203 

Others to their assuming ft crystalline or true 
granitic structure; but it is also ascertaiaed by 
experiment) that the same materials may, under 
different circmnstancesy form very different rocka, 
The same lava, for example, may be glassy, or 
scoriaceous, or stony, or porphyritic, according to 
the more or less rapid rate at which it cools ; and 
some trachytes and syenitic-greenstones may 
doubtless form granite and syenite, if the crysh 
tallization take place slowly. 

It would be easy to multiply examples and 
authorities to prove the gradation of the granitic 
into the trap rocks. On the western side of the 
fiord of Christiania, in Norway, there is a large 
district of trap, chiefly greenstone-porphjnry, and 
syenitic-greenstone, resting on fos^iliferous strata. 
To this, on its southern limit, succeeds a region 
equally extensive of syenite, the passage from the 
volcanic to the plutonic rock being so gradual 
that it is impossible to draw a line of demarcation 
between them, 

** The ordinary granite of Aberdeenshire," says 
Dr. MacCulloch, ^^ is the usual ternary compomid 
of quartz, felspar, and mica ; but sometimes horn* 
blende i3 substituted for the mica. But in many 
places a variety occurs which is composed simply 
of felspar and hornblende ; and in examining more 
minutely this duplicate compound, it is observed 
in some places to assume a fine grain, and af 

%'6 



kngth t6 become undistingtiifthabk frbm tlie 
greenstones of the trap &mily. It also passes in' 
thfe s^ime uninterrupted manner into a basahj and 
at length into a soft claystone, with a schistose 
tendency on exposure, in no respeiet differing 
from those. of the trap islands of the westsm 
coast"* The same author mentions, that in 
Shetland, a granite composed of hornblende, mica, 
felspar, and quartz, graduates in an equally perfect 
manner into basaltf . 

In Hungary there are varieties , of trachyte, 
which, geologically speaking, are of modern origin, 
in which crystals, not only of mica, but of quartz, 
are common, together with felspar and hornblende. 
It is easy to conceive how such volcanic masses 
may* at a certain depth from the surface, pass 
downwards into granite. 

I have already hinted at the close analogy in 
the forms of certain granitic and trappean veins ; 
and it will be found that strata penetrated by 
plutonic rocks have suffered changes very similar 
to those exhibited near the. contact of volcanic 
dikes. Thus, in Glen Tilt,, in Scotland, alter-^* 
nating strata of limestone and argillaceous, schist 
come in contact with a. mass of granite. The 
contact does not take place as might have been 
looked for, if the granite had been formed there 

* Syst. of Geol.^ vol. up, .157. f tti^n P- 1^* 



CII.WU3 



Mtia^iTs ymijf^ 



900. 



before the strata were deposited^ in wUck eiuKi 
tjbe section would have appeared as in Fig. 11 Ij;. 
but the ujaion is as represented in Fig* 1 12., the 



Fig. ill. 




Jtmdion qf granite and argiUaceom »cki$t in Olen 
TUL (BCacCuUoch.)* 

undulating outline of the granite intersecting diC* 
ferent strata, and occasionally intruding itself in 
tortuous veins into the beds of clay-slate and 
limestone, from which it differs so remarkably 
in composition. The limestone is sometimes 
changed in character by the proximity of the 
granitic mass or its veins, and acquires a more 
compact texture, like that of hornstone or chert, 
with a splintery fi'acture, eflFervescing feebly with 
acids. 

The annexed diagram (Fig. 113.) represents 
another junction, in the same district, where the 
granite sends forth so many veins as to reticulate 
the limestone and schist, the veins diminishing 
towards their termination to the thickness of a 

• Gtol. Traos., Fir»t Series, vohiH. j)I,21. 



SOCKS ALTBBED 



leaf of paper or a tliread. In some places frag- 
ments of granite B[^)ear entangled; as it were, in 
the limeatooe, and are not visibly connected vpith 
any lai^r mass ; .while sometimes, on the other 
hand, a lump of the limestone is found in the 
pildst of the granite. The ordinary colour of 




a. Granite. S. LimeMone. 

c. Blue argillaceous schisl. 

die limestone of Glen Tilt is lead blue, and its 
texture lai^e-grained and highly crystalline ; but 
where it approximates to the grwiite, particularly 
where it is penetrate 1^ the smaller veins, the 



Cli.IX.3 ?Y GRANITE VBINS. 207 

crystalline texture disappears, and it assumes an 
appearance exactly rese^nbling that of bomstone. 
The associated argillaceous schist often passes 
into hornblende slate, where it approaches very 
near to the granite,* 

The conversion of the limestone in these and 
many other instances into a siliceous rock, effer-< 
vescing slowly with acids, would be difEcult of 
explanation, were it not ascertained that such 
limestones are always impure, containing grains 
of quartz, mica, or felspar disseminated through 
them. The elements of these minerals, when the 
rock has been subjected to great heat, may have 
been fused, and so spread more uniformly through 
the whole mass. 

In the plutonic, as in the volcanic rocks, there 
is every gradation from a tortuous vein to the 
most regular form of a dike, such as intersect the 
tuffs and lavas of Vesuvius and Etna. Dikes of 
granite may be seen, among other places, on the 
southern flank of Mount Battock, one of the 
Grampians, the opposite walls sometimes pre-? 
serving an exact parallelism for a considerable 
distance. 

As a general rule, however, granite veins in 
all quarters of the globe are more sinuous in 
their course than those of trap. They present 

• MacCidloch, Geol. Trans,, vol. iii, p. 259, 




GKANITE VZIVS. ITatl. 

similar shapes at the most 

^5 northern point of Scotland, 

. ^-. and the south^nmost ex- 

~\! '1 iz^^^^J- ^^^""^ of Africa, as the an- 

/!',■ \a s^,-a1-« nexed drawings will show. 

It is not uocommoa for 

^ one set of granite veins 

to intersect another; and 

?. sometimes there are three 

' sets, 83 in the environs 

« /r«iiiTJ*« iiuj «(a/e. of Heidelberg, where die 
si^.* granite on the banks of 

the river Necker is seen to consist of three 
varieties, differing in colour, grain, and various 
peculiarities of mineral composition. One of 
these, which is evidently the second in age, is 
seen to cut through an older granite ; and another, 
still newer, traverses both the second and the 
first. 

In Shetland there are two kinds of granite. 
One of them, composed of hornblende, mica, fel- 
spar, and quartz, is of a dark colour, and is seen 
underlying gneiss. The other is a red granite, 
which penetrates the dark variety evaywhere in 
veliu(.f 
. The accompanying sketches will expUuo t^. 

• Capt B. Hall, Trans. Boy. Soc. Edin., vol. vii. " 
' t MacCUlocb, 8]«. of Geoln vol. i. p. 50. 



fiSANITE VEINS. 



manner in which granite veins often ramify an 

cut each odier. (Figg, 115. and 116.) Tiieyi\ 

Fig. 115. 




CnBMtftHutrateT^mgtMia.C^eWlraa. (MuCiUlDcli. 



present the manner in which the gneiss at C^ 
Wrath, in Sutherlandshire, is intersected by veins. 
Their light colour, strongly contrasted with that 
of the hornblende-schist, here associated with the 
gneiss, renders them very conspicuous. 




(nwniivtiuMMCr^fOaMkAiSBSlaid: IMmCuDdA.) 



Granite very generally assumes a finer grain, 
and undei^oes a change in min»^ composkion. 



* Western lalandi, pi. 31. • 



tto 



HIMB&AX STKDCrUHE Of 



m the veins whkh it sends into contigqous rocka. 
Thus, according to Professiff Sedgvic^ the niain 
body of the Cornish granite is an aggr^ate of 
mica, quartz, and felspar ; but the veins are some- 
times without mica, being a gf anutar aggregate of 
quartz and felspar. In other varieties quartz pre- 
vails to the almost entire exclusion both of felspar 
and mica; in others, the mica and quartz both 
disappear, and the vem is simply composed of 
white granular felspar. * 

Fig. 117. 




Fig. 117, is a sketch of a group of granite veins 
in Cornwall, given by Messrs. Von Oeynhausen 
and Von Dechen. f The main body of die granite 
here is of a porphyritic appearance, with lai^ 

* Od OeoL of Oomwall, TraDB. of Oambridge Soc., vol. i. 
p. 1S4. 
f Phil. Mag. BDd AdtibIb, No. S7. New Series, March, 



CklX.] GBAHITK III VKItn. gj) 

OTBtak of felspar; but in die veins it is &ie- 
grdned, and tdtbout the§e large crystals. Hie 
general height c^ the yeins is from sixte«i to 
twenty feet, but scKne are much bighw. 

In the Valorsine, a valley not far from Moat 
Blanc, in Switzerland, an ordinary granit^ con- 
sbting of felspar, c|uaitz, and mica, sends forth 
Teins into aOalcose gneiss (or stratified prott^ine), 
and in some places lateral ramifications are thrown 
ofi^ from the principal veins at right angles (see 
Fig. 118.) the reins, especially the minuter ones, 
beii^ finer grtuned thaQ the gramte in mass. 



It is here remarked, thi^t the schist and granite 
as th^ i^proach, seem to exercise a reciprocal 
influence on each other, for both undergo a modi- 
fica^on of mineral character. Tbe granite still 
remaining imstratified, becomes charged widi green 
particles ; and the talcose gneiss assumes a grani- 
tiformt structure, without losing its stratification.* 

* Necber, nir la V^. de Valornae, M£m. de la Soc. de 
Phfs, de G^n^e, I828.-r-I vkited,)a lS32,tbe spot reEerred 
to in Fig. 118, 



I^lg IfiBVALS NfiAR t^RANtTE. C^rt't 

,-. Profi^sor* Kdlfaou drew my attention to severed 
lociiUties in the oountry near Christiania, where 
ttie mineral character of gneiss appears to hd^re 
been affected by a granite of mudi newer origin, 
for some di3tance from the point of contact. 
The gneiss, without losing its laminated structui^e, 
seems to have become charged with a larger quan- 
tity of felspar, and that of a redder colour, than 
the felspar usually belonging to the gneiss of Nor* 
way. 

Granite, syenite, and those porphjrries which 
have a granitiform structure, in short all plutonic 
rocks, are frequently observed to contain metals, at 
or near their junction with stratified formations. 
On the other hand, the veins which traverse stra- 
tified rocks are, as a general law, more metalli- 
ferous near such junctions than in other positions. 
Hence it has been inferred that these metals may 
have been spread in a gaseous form through the 
fused mass, and that the contact of another rock, 
in a different state of temperature,* or sometimes 
the existence of rents in other rocks in* the vicinity, 
may have caused the sublimation of the metals. * 

There are many instances, as at Markerud, near 
Christiania, in Norway, where the strike of the 
beds has not been deranged throughout a large 
area by the intrusion of granite, both in large 
masses and in veins. This fact is considered by 

* Keeker, Proceedings of GeoL Soc, No. 26. p. 392. 



Ch.lX.} ISOLATED HASSEB OF, GBAHITE. S|^ 

pome ^ecJc^ste to militate agaiiut the theory of 
the forcihie injection of granite in a fluid stat«; 
But it may be stated in reply, diat ramifying 
akee of trap, which almost all now admit to have 
been once fluid, pass through the same fosnliie* 
roue strata, near Christiania, without deranging 
their strike or dip. * 

The real or apparent isolation of large or small 
masses of granite detached from the main body, as at 
a b, Fig.119^ and aboTe,Fig. 113., and a. Fig. 118., 




has been thought by some writers to be irrecon- 
cilable with the doctrine usually taught respect- 
ing veins; but many of them may, in fact, be 
sections of root-shaped prolongations of granite; 
while, in other cases, they may in reality be de- 
tached portions of rock having the plutonic stru&-, 
ture. For there may have been spots in the midst 
of the invaded strata, in which there was an as- 
semblage of materials more fusible than the rest,. 

t See Keilhau'B Gffla NoTvcgica ; Cliri»tipnia, 1836.- 



S14 



QUAKTZ VC1K& 



or moie fitted to combine readily iato some form 
of granite. 

Veins of pure quartz are often found in granite, 
«8 in many stratified rocks, "but iLey are not trace- 
able, like veins of granite or trap, to large bodies 
of ro<^ of Bimilar composiiion. They a^^iear Id 
bave been cracks, into which siliceous matter was 
infiltered. Such segregation, as it is called, can 
sometimes be shown to have clearly taken place 
long subsequently to the original consolidation of 
the containing rock. Tbus, for example, in the 
gneiss of Tronstad Strand, near Drammen, in 
Norway, the annexed section is seen on the beach. 

Fig. 120. 




It appears that the alternating strata of whitish 
granitiform gneiss, and black hornblende-schist, 
■were first cut through by a greenstone dike, about 
2^ feet wide ; then the track a b passed through 
all these rocks, and was filled up with quartz. 
The opposite walls of the vein are in some parts 



Ch. IX] CONFOBUABLE FORPHTBHSL 216 

incrusted with transparent crystals of quartz, the 
middle of the vein being filled up with common 
opaque white quartz. 

We have seen that the volcanic formations have 
been called overlying, because they not only pene- 
trate others, but spread over them. Mr. Necker 
has proposed to call the granites the underlying 
ijgneous rocks, and the distinction here indicated 
is highly characteristic. It was indeed supposed 
by Von Buch, at the commencement of his geolo- 
gical career, that the .granite of Christiania, m 
Norway, was sometimes intercalated in mountain 
masses between the transition strata of that coun- 
try, overlying fossiliferous shale and limestone. 
But although the granite sends veins into these 
fossiliferous rocks, and is decidedly posterior in 
origin, the opinion expressed of its actual si^r- 
position in mass has been disproved by Professor 
Keilhau, some of whose observations Respecting 
localities referred to by Von Buch, I have lately 
had opportunities of verifying. There are, how- 
ever, on a smaller scale, certain beds of euritic 
porphyry, some a few feet, others many yards in 
thickness, which pass into granite, and deserve 
perhaps to be classed as plutonic rather than 
trappean rocks, which may truly be described as 
interposed conformably between fossiliferous strata, 
as the porph3rries {a c. Fig. 121.), which divide the 
bituminous shales and argiUaceovis limestones, y*£ 



216 



OOVFOBMABLE FORPHYRIE& 



CPwtt 



Fig. ISl. 




SttriHe porpl^ry aUenuUIng withfossiltferout tnmtition strata, 

near Ckristiania, 

But some of these same porphyries are partially 
miconformable, as h, and may lead us to suspect 
that the others also, notwithstanding their appear- 
ance of interstratification, have been forcibly in- 
jected. Some of the porphyritic rocks above 
mentioned are highly quartzose, others very fels- 
•pathic. In proportion as the masses are more 
voluminous, they become more granitic in their 
texture, less conformable, and even begin to send 
forth veins into contiguous strata. In a word, we 
have here a beautiful illustration of the interme* 
diate gradations between volcanic and plutonic 
rocks, not only in their mineralogical composition 
and structure, but also in their relations of posi- 
tion to associated formations. If the term over- 
lying can in this instance be applied to a plutonic 
rock, it is only in proportion as that rock begins 
to acquire a trappean aspect. 

It has been already hinted that the heat, which 
in every active volcano extends downwards to in- 
definite depths, must produce simultaneously very 
different effects near the sur&ce, and fiur below it ; 
and we cannot suppose that rocks resulting firom 



r 



Ch. IX.3 GRANITIC ROCKS. 217 

the crystallizing of fused matter under a pressure 
of several miles of. the earth's crust can resemble 
those; formed at or near the surface. Hence the 
production at great depths of a class of rocks ana- 
logous to. the volcanic, and yet differing in many 
particulars, might almost have been predicted, 
even had we no plutonic formations to account 
for. How well these agree, both in their positive 
and negative characters with the theory of their 
deep subterranean origin, the student will be able 
to judge by considering the descriptions already 
given. 

It has, however, been objected, that if the gra- 
nitic and volcanic rocks were simply different 
parts of one great series, we ought to find in 
mountain chains volcanic dikes passing upwards 
into lava, and downwards into granite. But we 
may answer, that our vertical sections are usually 
of small extent ; and if we find in certain places 
a transition from trap to porous lava, and in others 
a passage firom granite to trap, it is as much as 
could be expected of this evidence. 

The prodigious extent of denudation which has 
been already demonstrated to have occurred at 
former periods, will reconcile the student to the 
belief, that crystalline rocks of high antiquity, al- 
though deep in the earth's crust when originally 
formed, may have become uncovered and exposed 
at the surface. Their actual elevation above the 



218 GRAKITE. [Ptrt I. 

gea may be refim^ to ^t» same eaiises ta whidi 
we have attributed the ii{>heava) of marine strata, 
even to the suiiH&its of some mountain chains. 
But to diese and other topics, I shall rerert wben 
speaking, in the seeond part, c^ the relative ages 
<^ different masses <i^ granite. 



219 



CHAPTER X. 



HETAMORPHIC ROCKS. 



(General character of metamorphk rocks — Gneiss -^Hora- 
blende-schist -— Mica-schist — Claynslate — Quartzite *— 
Chlorite-schist — Metamorphic limestone — Alphabetical 
list and explanation of other rocks of this family — Origin 
of the metamorphic strata -—Their stratification is real 
and distinct from cleavage — On joints and slaty cleavage 
— Supposed causes of these structures — how far con- 
nected with crystalline action. 

We have now considered three distinct classes of 
rocks : first, the aqueous, or fossiliferous ; secondly, 
the volcanic ; and, thirdly^ the plutonie, or gra*- 
nitie ; and we have now lastly to examine those 
crystalline strata to which the name of metamar- 
pJuc has been assigned. The last>-mentioned 
term ex{»«sses, as before explained, a tli^oretical 
opnion that such strata, after having been de- 
posited from water, acquired by the influence of 
heat and other causes a highly crystalline tex- 
ture. 

These rocks, wboi in their most characteristic 
or normal state, are wholly devoid of organic re- 
mains, and coiitain no distinct fragznents of odier 
rocks whether rounded or angular. They some- 
times break out in the central parts of narrow 

L 2 



220 METAMORl>ktC ROCKS. eFart I. 

mountain chains, but in other cases extend over 
areas of vast dimensions, occupying, for example, 
nearly the whole of Norway and Sweden^ where, 
as in Brazil, they appear alike in tlie lower and 
higher grounds. In Great Britain those mem- 
bers of the series which approach mo«tt n^ady to 
granite in their ccHaipoBkion» aa gai^bafiy mica- 
schist and hornblende-schist, are confined to the 
country north of the rivers Forth and Clyde. 

Many attempts have been made to trace- a 
general order of succession or superposition in 
the members of this family ; gneiss, for example, 
having been often supposed to hold invariably a 
lower geological position than mica-schist* But 
although such an order may prevail throughout 
limited districts, it is by no means universal, nor 
even general throughout the gldbe. To this sub- 
ject, however, we shall again revert in the second 
part of this volume, when the chronological re- 
lations of the metamorphic rocks are pointed out. 

The following may be enumerated as the prin- 
cipal members of the metamorphic class, gneiss, 
mica-schist, hornblendenscbist, day-slale, chlorite- 
schist, hypogene or metamorphic limestone, and 
certain kinds of quarts rock or quartzite. 

Qneissi: — ^The first of tbese^ gneiss^ majr be 
called strlitified granite, being .fcnrmed. of doe 
same mavemls as grtmite^ nat»ely fdspao^iqnar&f 
and mica. In the ; specimen faerefigund^ ilfe 




FragttunI tif gtvittt tatitral Hze, uetkm at rtuhi anglti to fianet 



white layers consist almost exclusively of granular 
felspar, with hwe and there a speck of mica and 
gmn of quartz. The dark layers are composed 
of grey quartz and black mica, with occasionally 
a grain of felspar intermixed. The rock splits 
most easily in the plane of these darker layers, 
and die surface thus exposed is almost entirely 
covered with shining spangles of mica. The ac- 
companying quartz however greatly predominates 
in quantity, but the most ready cleavage is de- 
termined by the abundance of mica in certiun 
parts of the dark layer. 

Instead of these thin laminte gneiss is some- 
times- simply divided into thick beds, in which 
the mica has only a slight degree of parallelism 
to the planes of stratification. 

1^ t«rm ." gmnsB," however, ia geology is 
oommonly used in a wider senae to desigoiVte a 
formation iu' vhidi; the above mentioned rock 
prevails, . but with which any one of the other 



122t2 HORl^LEKDE-SCHtST. — MICA-SCHIST. [Part I. 

metamorphic rocks, and more especially horn- 
blende-schist, may alternate. These other mem- 
bers of the metamorphic series are, in this case, 
considered as subordinate to the true gneiss. In 
some rare instances fragments of pre-existing 
rocks may be detected in gneiss. 

TTie different varieties of rock allied to gneiss, 
into which felspar enters as an essential ingre- 
dient, will be understood by referring to what was 
said of granite. Thus, for example, hornblende 
may be superadded to mica, quartz, and felspar, 
formmg a syenitic gneiss; or talc may be sub- 
stituted for mica, constituting talcose gneiss, a 
rock composed of felspar, quartz, and talc, in 
distinct crystals or grains (stratified protogine of 
the French). 

Homblende^schist is usually black, and composed 
principally of hornblende, widi a variable quan- 
tity of felspar, and scmietimes grains of quartz. 
When the hornblende and felspar are nearly in 
equal quantities, and the rock is not slaXy, it cor- 
responds in character with the greenstones of the 
trap family, and has been called '*^ primitive green- 
stone." Some of these homblendic masses ms^ 
really have been volcanic rocks, which have since 
assumed a more crystalline or metamorphic tex- 
ture. 

MtcorBchist^ or micaceous ichiOj is, next to gneiss, 
one of the most abundant rocks of die 



Cb, XT CLAY^L ATS. - QUARTZITE. HSj^ 

pbic serieeu It is 3laty» essentially ccunposed ol 
mica and quartz, the mica sometimes appearing 
to ctmstitute the whole mass. Beds of pure 
quarta also oceur in this formation* In some dis- 
tricts garnets in regular twdve-sided crystals form 
an integrant pcurt of mica-schist. This rock passes 
by insensible gradadons into clay-slate. 

dajf^Iate^ <jt JrgiUaoewsschiit. — This rock re- 
sembles an indurated clay or shal^, is for the most 
part extremely fissile, often affording good roofing 
slate. It may consist <^ the ingredients of gneiss, 
or of an extremely fine mixture of mica and 
quartz, or talc and quartz. Occasionally it de- 
rivefi a shining and silky lustre from the minute 
particles of mica or talc which it contains. It 
varies from greeniah or bluiah-grey to a lead 
colour. It may be said of this, more than of any 
otb^r schist, that it is common to the metamorphic 
and fossiliforous series, for some clay-slates taken 
firom each division would not be distinguishable 
by mineralogical characters. 

QftartzitCj or Qtwrfz rochj is an aggregate of 
grains of quartz, which are cither in minute crys- 
tals, or in many cases slightly rounded, occurring 
in regular strata associated with gneiss or other 
metamorphic rocks. Compact quartz, like that 
so fi-equently found in veins is also found together 
widbi granular quartzite. Both of these alternate 

L 4 



224 HYFOOElfB XillffitnxmE. [Partl. 

witk gndss dr micftHsfdiist^ err pass into those rocks 
by the addition of mica, or of (ekpsm and mica. 

Chhrit&'Schist is a green slaty rock in 'trhich 
chlorite is abundant in foliated plates, usually 
blended with minute grains of quartz, or 'Sinne- 
times with felspar or mica. Often associated with, 
and graduating into, gneiss and clay-slate. 

Hypogene or metamorphie limeslxm. ~ This rock, 
commonly called primary limestone, is sometimes 
a thick bedded white crystalline granular marble 
used in sculpture; but more firequently it occurs 
in thin beds, forming a foliated schist much re- 
sembling in colour and appearance certain varie- 
ties of gneiss and mica-schist It alternates with 
both these rocks, and in like manner with argil- 
laceous schist. It then usually contains some 
crystals of mica, and occasionally quartz, felspar, 
hornblende, and talc. This member of the meta- 
morphie series enters sparingly into the structure 
ofthehypogene districts of Norway, Sweden, and 
Scotland, but is largely deyeloped in the Alps. 

Before offering any further observations on the 
probable origin of the metamorphie rocks, I sul>- 
join in the form of a glossary, a brief explanation 
of some of the principal varieties and their syno- 
nymes. 

AomiOLira«scHi«T. A <laty /oiiated rock, compCMcd chieflj of 
actinolite, (an emendd-green mineral, allied to hornblende,) 
with some admixture of fi^spfur, or quartz, or miea. 



Ch. X.] MJBSJAlieRrHie iioeK& 

Anf^iTJi. ^luminous slate, (Broiigiuiupl)^ o«cun fawtb iH'tbe 

metamorphic and fosiuliferous series. 
Aif^BiBOLiTC. Horablende rock, which see. 
Aaoivi.ACioes-sciu8Ty or Clat«4Latx» See p. d2S« 

Cbiastolitk-slatx scarcely differs from clay-slate, but includes 
munerous crystals of Chiastolite; In considerable thickness 
in Cumberland. Chiastolite occurs in long slender rbent** 
boidal crystals. For composition, see Table, p. 166. 

Chlobits-schist. a green slaty rock, in which chlorite, a green 
scaly mineral, is abundant. See p* 224« 

Clat-slatk, or Aroillacbous-schist. See p. 223. 

EuMTX and Euritic Porphyry. A base of compact felspar, with 
grains of laminar felspar, and often mica and other minessls 
disseminated (Brongniart). M. D'Aubuisson regards eurite 
as an extremely fine grained granite, in which felspar pre- 
dominates, the whole forming an ai^sarently homogeneous 
rock. Eurite has been already mentioned as i^plutotuc rocbi 
but occurs also in beds subordinate to gneiss or mica-slate. , 

GvBiss. A stratified or laminated rods:> same composition as 
granite. See p. 220. 

HoRNVLSMDE Rocx, or Amphibolitx. The same composition as ' 
hornblende schist, stratified, but not ^ssile. See p* 163. 

HoRNBLBNDE-scHXST, or Slate. Composed chiefly of hornblende, 
with occasionally some felspar. See p. 222. 

HoRVBLXNBic or Syxnitic Gnxiss. Composed of felspaT) qmsttiy 
and hornblende. 

Hypogxnx Lihxstome. See p. 224. 

Marblx. See p. 224. < 

MicA-scHisT, or MicAcxous-scHiST. A slaty rock» composed .of 

mica and quartz in variable proportions. See p. 222. 
MzcA-SLATX. See Mica-schist, p. 222. 

Phyilai^x. D* Aubuiason's term for clay^late, from ^vAAoi) 'a 

beap of leaTes. 
Primary LiitxsTOMX. See Hyvoomx LzkistOick, p. 224; 

L 5 



236 MfiTAMOBPHlC fiOCXS; {ButL 

pAOTbGiNK. See TALOMs-ewiEisiy' p. 222. t wbeii imstrfltifi«A it h 
Tticote-gntmte, 

Quartz Rock, or Quartzitk. A stratified rode ; an aggtegite 
of grains of quartz. See p. 223. 

Sb&pxntinx occurs in both dmsions of the h)fpogene series, as 
a stratified or unstratified rock ; contains much magneaa ; 
is cliiefl J composed of the rainend called serpetttine, mixed 
with diallage, taic, and steatite. The pure varieties of this 
rock, called noble serpentine, consist of a hydrated alicate 
of magnesia, generally of a greenish colour; tfaia base is 
commonly mixed with oxide of iron. 

TalcosE'Gneiss. Same composition as taleose gmnhe or pro- 

togine, but either lAradfied or laminated^ 
Talcosx-schist consists chiefly of talc, or of talc and qttartz, 

or of talc and fslspar, and has a texture something like that 

of clay-slate. 

Whitxstonx. Same as Eurite. 



Or iff in of the Metamorphic Strata. 

Having said thus much of the mineral com- 
position of the metamorphic rocks, I may combine 
what remains to be said of their atructure and 
history, with an account of the opinions enter- 
tained of their probable origin. At tlie same 
time it may be well to forewarn the reader ttat 
t<re are here entering upon ground of controversy, 
and soon reach the limits where positive inductioB 
ends, and beyond which we can only indulge in 
speculations. It was once a favourite doctrine, and 
is still maintained by many) that these rocks owe 



Ch.Z:3 AND THBIR ORIGIN. 227 

their crjitBlalliiie texture, dieir want of all signs of 
a mechanical origin, or of fossil eantents, to a 
peculiar and nascent condition of tbe planet at 
die period of tbrir formation. The arguments 
in refutation of this hypothesis will be more fully 
considered when I show, in the second part of 
this volume, to how many diffi»reat ages the 
metamorphic formations are referable, and how 
gneiss, mica-schist, day»slate, and hypogene lime* 
stone (that of Carrara for example), havo been 
formed, not only since the first introduction of 
organic beings into this planet, but even long 
after many distinct races of plants and animals 
had passed away in succession. 

The doctrine respecting the crystalline strata, 
implied in the name metamorphic, may properly 
be treated of in this place ; and we must first in- 
tjuire whether these rocks are really ^ititled to 
be called stratified in the strict sense of having 
been originally deposited as sediment from water. 
The gaieral adoption by geoio^ts of the term 
stratified, as applied to these rocks, sufficiently 
attests their division into beds very analogous, at 
least in form, to ordinary fossiliferous strata. This 
TOsembfauoce is by no means confined to the exist- 
ence in bo& df an occasional sla^ structure^ but 
extends to every kind of arrangement which is 
compatible with the absence of fossils, and of sand, 
pebbles, ripple mark, and other characters which 

L 6 



228 OKlOIir OF'THB [Ftttl. 

the. metamorphic tlwoiy sapposes to have b^n 
obliterated hj plutonic action. Tbufiy ioc le^sL^ 
ampte) we behold alike in the crystallme and firo" 
siliferoos fbrmationB an alternation of beds varysa^ 
greatly in composition, colour, and thidbieBB. We 
observe, for instance, gneiss alternating with lay- 
ers of black hornblende-schist, or with granulai* 
quartz, or limestone ; and the interchange of these 
different strata may be repeated for aa indefinite 
number of times. In the like manner, mica^ 
schist alternates with chlorite-schist, and with 
granular limestone in thin layers. 

As in fossiliferous formations strata of pure 
siliceous sand alternate with micaceous sand and 
with layers of clay, so in the crystalline or meta- 
morphic rocks we have beds of pure quartzite alter- 
nating with mica-schist and clay-slate. As in the 
secondary and tertiary series we meet with lime- 
stone alternating again and again with micaceous 
or argillaceous sand, so we find in the hypogene, 
gn^ss and mica-schist alternating with pure and 
impure granular limestones. 

It has also been shown that the ri|^le mark is 
very commonly repeated throughout a considerdile 
thickness of fossiliferous strata, so in mitoredkifit 
and gneiss, there is sometimes an un^uladoB of 
the laminas on a minute scale, which may, per- 
haps, be a modification of similar inequalities in 
the original deposit. 



a. X-l HBTAKOBSHK KOCK& gjf 

Id line ciTBtaUaae finma^ons alsvt asio aianji 
of the fiedimentaif bdbre denmbed, sitt^e ntnte 
are sometnnes made up of lamiiue placed (tiiga« 
TuMy, Bach laminaa not being r^ulaily parallel to 
the pluies of deavage. 

This disposition of the layers is illustrated^ib 
the accompanying diagram, in which I have Fe- 

Flg. 198. 




presented carefully the stratification of a eoamw 
ai^llaceous schist, which I examined in dhe 
Pyrenees, part of which approaches in charaeMr 
to a green and blue rooting slate, while part is 
extremely quartzose, the whole mass passing downt- 
wards into micaceous eclust. The vertical setcian 
here exhibited is about three feet in hdght, and 
the layers are sometimes so thin that 6£sy nny be 
counted in the tUckness of an inch. Soide-cf 
them con^t of pure quartE. • -. -i, 

The infereBce 'drawn £tom the 'phenomena 
aixire described, in favour of dile aqueous oti^ 
of clay-slate and ether crystalline atrata, is greody 



280r 0LktT ct;«ATAO£. ' [ebti. 

strengtfaei^ by the fiiet ll»t many of these ne- 
tamorpbic rocks ooeasiomfly attemate wtth^ and 
sometimes pass, by intermediate gradations, into 
rocks of a decidedly mechanical origin, and ex* 
hibiting traces of organic remains. The fessil- 
iferons formations, moreover, into whi^ this pas- 
sage is effected, are by no means invariably of tbe 
same age nor of the highest antiquity, as will be 
afterwards explained. (See Part IL) 

Stratification of the metamorphic rocks distinct 
from cleavoffe. — The beds into which gneiss, mica- 
schist, and hypogene limestone divide, exhibit 
most commonly, like ordinary strata, a want of 
perfect geometrical parallelism. For this reason, 
therefore, in addition to the alternate recurrence 
of layers of distinct materials, the stratified ar- 
rangement of the crystalline rodcs cannot be ex- 
plained away by supposing it to be simply a 
divisional structure like that to which we owe 
some of the slates used for writing and roofing. 
ISeOy deaiooffe as it has been called, has in many 
cases been produced by die regidar deposition of 
thin plates of fine sediment one nqpon another, 
but tiiere are many instances where it is decidedfy 
unconnected with such a mode of origin, and 
where it is not even confined to dae aqueous form- 
ations. Some kinds of trap, for example, as clink- 
stone, split into laminae, and are used for roc^ng. 

Hiere are, says Professor Sedgwick, diree dis^ 



t - 



Cb.X.] JOIKTED STROCTUHE. QSI 

tinct forms of structure e^dnbited in certsdn rocks 
dirotighout large districts : vie* — First, stratifica* 
tion ; t»econdly, joints ; and thirdly, slaty cleavage ; 
tlie tmo last having no connection with true bed- 
ding, and having been superinduced by causes 
absolutely independent of gravitation. All these 
difik^ent structures must have diflferent names, even 
though there be s<Mne cases where it is impossible, 
afi:er carefully studying the appearances, to decide 
upon the class to which they belong. * 

Joints. — Now in regard to the second of these 
forms of structure or joints, diey are natural 
fissures which often traverse rocks in straight and 
well determined lines. They afibrd to the quarry- 
man, as Mr. Murchison observes, when speaking 
of the phenomena, as exhibited in Shropshire and 
the neighbouring counties, the greatest aid in the 
extraction of blocks of stone, and, if a sufficient 
number cross each other, the whole mass of rock 
is split into symmetrical blocks, f The &ces of 
the joints are for the most part smoother and 
more regular than the surfaces of true strata. 
The joints are JStraight->out chinks, often slightly 
cfp&i, often passmg, not only through layers of 
successive deposition, but also through balls of 
liBnestone or odier maUer which have been formed 

• Geol. Trans., Second Series, vol. iii. p. 480. 
f The SUurian System of Rocks, as developed in Salop, 
Hereford, Sec, p. 245. 



233 CLEATAOE AND JOINTS. [PutT. 

b;. concretionary action, since t^ or^;inal afiw- 
mulation of the strata. Sucb joints th^^fo^^ 
must often have resulted from one of the last 
changes «uperinduced upon sedimeDtary d^osits.* 
In the annexed diagram the flat sur&ceg ^ 
rock A, B, C, represent exposed faces of joints, to 
which the walls of other joints, J J, are parallel. 
S S are the lines of stratification ; C C are lines 
of daty cleavage, which intellect the rock at a con- 
siderable angle to the planes of stratification. 
Fig. 1S4. 




fiAvJtIcafJiw, JoJute mad dcarate. ' 

Joints according to Professor Sedgwick are dis- 
tinguishable from lines of slaty cleavage in this, 
that the rock intervening between two joints has 
no tendency to cleave in a directitxi paralld to 
the planes of the joints, whereas a rock is capable 
of indefinite subdivision in the direction of its 
alaty cleavage. In some casee where the strata 
are curved, the planes of cleavage are still per- 

* Tke Klnnnt S;Btcai of Rocks, M ierdopai m Sdop, 
Hereford, &c., p. S4S. 



Ch. X.] SLATY CLEAVAGE. 233 

fectly parallel. Thia has been observed in the 

slate rocks of part or Wales. (See Fig. 125.)wlucli 

Fig. 12J. 




c4ttraUi (Scilfvlck.] 

consist of a hard greenish slate The true bed- 
ding IS there indicated by a number of parallel 
stnpes, some of a lighter and some of a darker 
colour than the general mass Such stripes are 
fouad to be parilkl to the true planes of stratifica- 
tion, where\ci thtse are manifested by npplemark, 
or by beds containing peculiar orgtmic remains. 
Some of the contoitud strata are of a coarse me- 
chanical structure, alternating with fine-grained 
crystalline chloritic slates, in which case the same 
slaty cleavage extends through the coarser and 
finer beds, though it is brought out in greater 
perfection in proportion as the materials of the 
rock are fine and homogeneous. It is only when 
these are very coarse that the cleavage planes 
entirely vanish. These planes are usually inchned 
at a very considerable angle to the planes of the 
strata. In the Welsh chains, for example, the aver- 
age angle is as much as fi:om 30° to' 40°. Some- 
times the cleavage planes dip towards the same 
point of the compass as those of stratification, but 
more frequently to opposite points. It may be 



234 JOIVTED STRUCn^E [Psrtl. 

Stated as a g^ieral rule, that when beds of coarser 
materials alternate with those composed of finer 
particles, the slaty cleavage is either entirely con- 
fined to the fine-grained rock, or is very imper- 
fectly exhibited in that of coarser texture. This 
rule holds, whether the cleavage is parallel to the 
planes of stratification or not. 

In die Swiss and Savoy Alps, as Mr. Bakewell 
has remarked, enormous masses of limestone are 
cut through so regularly by nearly vertical part* 
ings, and these are often so much more conspi- 
cuous than the seams of stratification, that an 
unexperienced observer will almost inevitably 
confound them, and suppose the strata to be per- 
pendicular in places where in fiict they are almost 
horiK<»ital.* 

Now these joints are supposed to be analogous 
to those partings which have been already oh' 
served to separate volcanic and plutooic rocks 
into cuboidal and prismatic masses. On a small 
scale we see day and star<di when dry sjdit into 
similar shapes, which is often caused by simple 
contraction, whether the shrinking be due to the 
evaporation of water, or to a change of tempara* 
ture. It is well known that many sandstones 
and other rocks expand by the application of mo- 
derate degrees of heat, and then contract again 

* Introdiiction to Geology, diwp, h. 



C31.X] m ROCR& 285 

on cooling; and there can be no doubt that large 
portions of die earth's crust have, in the eourse of 
past ages, been subjected again and again to very 
difierent degrees of heat and cold. Hiese alter- 
nations of temperature have^ probably contributed 
largely to the production of joints in rocks. 

In some countries, as in Saxony, where masses 
of basalt rest on sandstone, the aqueous rock has 
for die distance of several fiset from the pmnt of 
junction assumed a columnar structure similar 
to that of the trap. In like manner some hearth- 
stones, after exposure to the heat of a fiimace 
without being melted, have become prismatic. 
Certain crystals also acquire by the application of 
heat a new internal arrangement, so as to break 
in a new direction, their external form remaining 
unaltered. 

Sooresby, when speaking of the icdbergs of Spits- 
bergen, states that ** they are full of rents, extend- 
ing perpendicularly downwards, and dividing them 
into innumerable columns." Colonel Jackson, who 
has lately investigated this subject more atten- 
tively, foimd that the ice on the Neva, at St. Peters- 
burg, at the beginning of a thaw, when two feet 
in thickness, is traversed by rows of very minute 
ahvbubbles extending in straight lines, sometimes 
a little inflected, from the upper surface of the ice 
towards the lower, within from two to five inches 
of which they terminate. " Other blocks pre- 



286 JOINTED STRUCTURE [Parti. 

sented these bubbles united, so as to form cylin* 
drioBl iOanals, a litde thicker than a horsehair. 
Obflerying still further," be says, ^^ I ibnnd Uoieks 
in whidh'the process was more advanced, apMl two, 
three^ or more clefts, struck off in di£^ent direc- 
tions from the vertical veins, so that a section per- 
peodicular to the vein would represent in miniature 
the 8tar*formed cracks of timber. Finally, in some 
pieces, these cracks united from top to bottom of 
the veins, separating the whole mass into vertical 
prisms, having a greater or less number of sides. 
In this state a slight shock was sufficient to detach 
them ; and the block with its scattered fragments 
was in all respects the exact miniature resemblance, 
in ciystal, of a Giant's Causeway. The surface 
was like a tessdlated pavement, and the columns 
rose dose^ adhering and parallel, from the com- 
pact mass of a few inches at the under sur&ce. 
More or less time is required for the j»*Qcess, 
which I have since seen in all its different stages." * 

Here again we find the columnar or jointed 
structure in a solid mass, which had been sub- 
jected to great changes of temperature. 

It seems, therefore, that the fissures called jinnts 
may have been the result of different causes, as of 
some modifioaticm of crystalline action, or simple 
contraction during consolidation, or during a 

* Joum. of Rojc. Oeogr^ph. See., vol.y« p. 19. 



ClhX.] AND CtffiAVAGE. 387 

chiur^e (ȣ temperature. And there are cifies 
where joints may have been due to meohanicd 
violence) and the strain exerted on strata duiriiig 
their upheaval, or when they have sunk down 
.bdow their former level. Professor Phillips 
has suggested that the previous existence of divi* 
sional > planes may often have determinedy and 
must gready have modified, the lines and points 
of fraoture caused in rocks by those foroes to which 
they owe their elevation or dislocations Thed6 
linlds and points being those of least resistance^ 
cannot fail to have influenced the dii^ection m 
which the solid mass would give way on the ap^ 
^ieat^m of external force. ^ 

It has been observed by Mr. Murchisoin, that 
in referring both joints and slaty cleavage to ciys^ 
tailine action, we are borne out by a well-known 
analogy in which crystallization ha« in like num. 
ner given rise to two distinct kinds of structure in 
the same body. Thus for example, in a six-isided 
prism ,of quartz, the jdanes of cleavage are dis- 
ttnot from those of the prism. It is impossible itd 
cleave the eiyslals parallel to tiie- plane of tiie 
prism, just as slaty rocks cannot be dieaved |)a- 
mUeL to ibe Joints, but the quartz crystal, like 
the older schists, may be cleaved ad in/initum>ixL 
tiie^directian of tlie cleavage planes* "^ 

* Silurian System o£ Rocks, &c., p. 246. 



ORIQIK (Xt [Fart I. 

I have already stated that extreme^ fine slaieBy 
like those of the Niesen, near the Lake-of Tbun, 
in Switzeckaidy are perfectly parallel to the planes 
of stratificati<m» and are, therefore^ probably due 
to EueoessiTe aqueous deposition. Even whoi the 
slates are oMique to the genend planes of the 
strata, it by no meaua follows as a matter of course^ 
that they hare been oaused by crystalline action, 
fiir they may be the result of that diagonal lami- 
nation which I have before described (p. 3Q»). 
In this case, however, there is usually mudi irre- 
gularis, whereas those cleavage planes oblique to 
the true stratification, which are referred to a crys- 
talline action, are often perfectly symmetrical, and 
observe a strict geometrical parallelism, even when 
the strata are contorted, as already described 
(p. 238.). 

In regard to the origin of slaty cleavage^ where 
it is unconnected with sedimentary deposition, 
Professor Sedgwick is of opinion that no retreat 
of parts, no ccmtraction in dimensions, in passing 
to a solid state, can account for the [^enmnenon. 
It must be referred to crystalline or polar forces 
acting simultmeoosly and somewhat uniformly, in 
given directions, on large masses having a homo- 
geneous oompositien. 

A fact recorded by Mr. Darwin afibrds con- 
firmation to this theory. The ore of the gold 
mines of YaquQ, in Chili, is ground in a mill into 



Ch,X,2 SLATT CLEAVAGK 289 

an impolpalde powder* Afteir this powder fan 
he&at washed^ and nearh^ all the meial separated^ 
Ae mud which passes from the miUa is collected 
into poolsy ^ere it subsides, and is deaied out 
and thrown into a common hei^ A great deal 
of chemical action dien commences^ salts of t»- 
rious kinds effloresce on the sur&ee^ and the mass 
becomes hard, and divides intoconcretionarj frag- 
ments. These fragments were observed to possess 
an even emd well defined daty structure; but the 
lamina? were not inclined at any uniform ai^le.* 

Mr. R. W. Fox lately submitted a mass of moist 
<^y, worked istp widi aeidukted wat^ to weak 
voltaic action for some mcmths, and it was found 
when dry to be rudely laminated, the phmes c^ 
the slightly imdulating laminae being at right 
angles to the direction of the electrical forces, f 

Sir John H^sdbel, in allosicm to slaty cleavage, 
has suggested, *' that if rocks have been so heated 
as to allow a commencement of crystallization; 
that is to say, if they have been heated to a point 
at which the particles can begin to move amongst 
themselves, or at least on their own axes, some 
genial law must then determine the position in 
which these particles will rest on cooling. Pro- 

* Journal, p. 324. (for title, see note p. 137.). 

f Although the lamination in the specimen shown to me 
was very imperfect, it was sufficiently evident to encourage 
farther experiments. 



240 SLATT CLEAVAGE. [Part I. 

bably, that position will have some relation to the 
direction in which the heat escapes. Now,, when 
all, or a majority of particles of the same nature 
have a general tendeqicy to one position, that 
must of course determine a cleavage plane. Thus 
we see the infinitesimal crystals of firesh preci- 
pitated sulphate of baryte^ and some other such 
bodies, arrange themselves alike in the fluid in 
which they float; so as, when stirred, all to glaiice 
with one light, and give the appearance of silky 
filaments. Some sorts of soap, in which insoluble 
margarates * exist, exhibit the same phenomenon 
when mixed with water; and what occurs in our 
experiments on a minute scale niay occur in na- 
ture on a great one.*' f 

♦ Margaric acid is an oleaginous acid, formed from differ- 
ent animal and vegetable fatty substances. A margarate is a 
compound of this acid with soda, potash, or some other base, 
and is so named from its pearly lustre. 

t Letter to the author, dated Cape of Good Hope, 
Feb. 20. 1836. 



241 



CHAPTER XL 

MET AMORPHIC itocKs -^ continued. 

Strata near some intrusive masses of granite converted into 
rocks identical with different members of the metamorphic 
series — Arguments hence derived as to the nature of 
phitonic action-— Time may enable this action to pervade 
denser masses '— From what kinds of sedimentary rock 
each variety of the metamorphic class may be derived — 
Certain objections to the metamorphic theory considered. 

It has been seen that geologists have been very 
generally led to infer, from the phenomena of 
joints and slaty cleavage, that mountain masses, of 
which the sedimentary origin is unquestionable, 
have been acted upon simultaneously by vast crys- 
talline forces. That the structure of fossiliferous 
strata has often been modified by some general 
cause since their original deposition, and even 
subsequently to their consolidation and disloca- 
tion, is undeniable. . These facts prepare us to 
believe, that still greater changes may have been 
worked out by a greater intensity, or more pro- 
longed development of the same agency, com- 
bined, perhaps, with other causes. Now we have 
seen that, near tJie immediate contact of granitic 
veins and volcanic dikes, very extraordinaiy alter- 
ations in rocks have taken place, more especially 

M 



242 * ALTERATIONS OF STRATA tPMtl. 

in the neighbourhood of granite. It will be use* 
fill here to add other illustrations, showing that 
a texture undistinguishable &om that whieh aha* 
racterizes the more crysteJfine metamorphic form- 
ations, has actually been superinduced in strata 
once fossiliferous. 

In the southern extremity of Norway, there is a 
large district, on the west side of the fiord of Chris- 
tiania, in which granite or syenite protxiuiles in 
mountain masses through fossiliferotis strata, and 
usually sends veins into them at the point of con- 
tact. The stratified rocks, replete with shells and 
zoophytes, consist chiefly of shale, Iknestotie) and 
some sandstone, and all these are invariably altered 
near the granite for a distance of from 50 to 404^ 
yards. The aluminous shales are haardened and have 
become flinty. Sometimes they resemble jasper* 
Ribboned jasper i» produced by the burdening' of 
alternate layers of green and chocolate-coloured 
schist, each stripe faithfully representing the oi^ 
ginal Hnes of stratificatioQ. Nearer the granite 
the schist often contains crystab oi hornblende^ 
which are even met with in smne {daces for a dis- 
tance of several hundred yards fi*om the junction; 
and this black hornblende is so abundant^ that 
eminent geologists, when passing through the 
country, have ccHifounded it with the anciex&t 
hornblende-schist, subordinate to the great gneiss 
formation of Norway. Frequently, betweesr the 



ClkXU IH COMIACT WUH ORAXtTB. Q^ 

giwute and the hombleadic slate, above jaea.' 
iiaaed, grains ef miea flod cryatalline fekpv (q»- 
{tear kt the aebis^ se that rocks lesemhling gueisa 
Bwi ttiics'^Bluat luie pfot^ced. Fosale can rarely 
het detected in t^eae ichists, and they are more 
completely e&ced in proportion to the more ccy^ 
laUise teedJire of the beds, and th<ac vicinity to 
tlie gtanite. In aOme places the sUiceouB matter 
of the schist becomes a granular quarts, and vthea 
bemblendle- and mica are added, the altered rock 
Jdsee its stratiHcation, and passes into a kind of 
grmile. The limestone, which at points remota 
frwa the granite is of an earthy t«(Xure, blue 
ooknir, and efien abounds in cor^s, becomes a 
white gtBnnlar marble near the granite, aometimeB 
ailieeou^ the gianular structure exteadtng occa^ 

Kg. 196. 




tdxmei^f/iMBifcrimi^aUiaidlttiiaUiitiiaH'fTiaile. Ctntitiuiii. 
The UTOWB indicate'the dip, and tbe ilrught lines the aUike, 
of Ifaebeda. 

sionally upwards of 400 yards &om the junction ; 
and the corals b^g for die most part obliterated. 



244 ALTERATIONS OF STRATA [Ftttl. 

though sometimes preserved, ev&k in the white 
marble. Both the altered limestone and hardened 
slate c<Hitain garnets in many places^ also^res of 
iron, lead, and copper, with some »lyer. These 
alterations occur equally, whether the granite in- 
vades the strata in a line parallel to the general 
strike of the fossiliferous beds, or in a line at right 
angles to their strike,' as will be seen by the ac- 
companying ground plan. * 

The indurated and ribboned schists above men;^ 
tioned, bear a strong resemblance to certain shales 
of the coal found at Russell's Hall, near Dudley, 
where coal mine£( have been on fire for ages. Beds 
of shale of considerable thickness, lying over the 
bumii^ coal, have been baked and hardened so 
as to acquire a flinty fracture, the layers being 
alternately green and brick-coloured. 

The granite of Cornwall, in like manner, sends 
forth veins into a coarse argillaceous-schist, pro- 
vincially termed killas. This killas is converted 
into hornblende-schist near the contact with the 
veins. These appearances are well seen at the 
junction of the granite^nd killas, in St. Michael's 
Mount, a small island nearly 300 feet high, situated 
in the bay, at a distance of about three miles from 
Penzance* 

The granite of Dartmoor, in Devonshire, says 

• Keilhau, Gaea Nonregica, pp. 61 — 63. 



Ch.XI.] W CONTACT WITH GRANITE. 245 

Mr/De la Becfae, has intruded Kself into the slate 
and daty sandstone called' grey wacke, twisting and 
dontbrting the strata^ and sending veins into them* 
Hehee scmie of the slate rocks hare become ^^ mi* 
caceous, others more indurated, and with the cha- 
ractei*s of mica-slate and gneiss, while oth«*s again 
appear cbnverted into a hard-zoned rock strongly 
impregnated with' felspar." * 

We learn &om the inyestigatioris of M. Du* 
ficfinoy, that "in the eastern Pyrenees there are 
motmtain masses of granite posterior in date to 
liie formation called lias and chalk of that district) 
and that these fossiliferous rocks are greatly altered 
in texture, and often charged with iron-ore, in the 
neighbourhood of the granite. Thus in the en- 
virons of St. Martin, near St. Paul de F^ouQlet^ 
the chalky limestone becomes more crystalline 
and saccharoid as it approaches the granite, and 
loses all traces of the fossils which it previously 
contained in abundance. At some pointSr misf^ it 
becomes dolomitic, and filled with small veins of 
carbonate of iron, and spots of red iron-ore. At 
Rancid* the lias nearest the granite is not only 
filled with iron-ore, but charged with pyrites, 
tremolite, garnet, and a new mineral somewhat 
allied to felspar, called, fix>m the place in the 
Pyrenees where it occurs " couzeranite." 

• * 

* Geol. Manual, p. 479. 
M 3 



246 PLUTONIC ACnOK EPirtl 

Now the altenrdons Aave desetibeA hb super- 
induced in rocks by Tolcamc dik^ and granite 
y^^ns, prove inoontestably diat powers exist m ru^ 
ture capable of transforming fossxtiferous into 
crystalline strata, — pow^-s capable of generating 
in them a new min^al ciiaraeter, similar, nay, 
often absolutely identical widi that of gneiss, 
mica-schist, and other stratified memb e rs of tiie 
hypogene series. Hie precise nature of these 
altering causes, which may provisionally be termed 
plutonic, is in a great degree obscure and doiibt- 
ful ; but their reality is no less clear, and we must 
suppose the influence of heat to be in some way 
connected with the transmutation, i^ for reasons 
before explained, we concede the igneous origin 
of granite. 

The experiments of Gregory Watt, in &sing 
rocks in the laboratory, and allowing them to 
consolidate by slow cooling, prove distinctly that 
a rock need not be perfectly melted in ord^ that 
a re-arrangement of its ^^omponent particles shouM 
take place, and a partial crystallization ensue. "* 
We may easily suppose, therefore, that all traces 
of shells and other organic remains may be do* 
stroyed ; and that new chemical eombiQations may 
arise, without the mass being so fused as that the 
lines of stratification should be wholly oblite- 
rated. 

♦ Phil. Trans. 1804. 



«ils;xj ^NAJTOvnc actios, ^7 



xsotr h^vfreveHf imagine that heat alone^ 
radi as nay be applied to a siKme in the open air, 
can congtituike .all that h comprised in plutonic ac- 
ticm. We kaow that Tolcanos in eruption not 
oidy ^emit ftoid lava, bat give off steam and odier 
beated-gases, -vhieh rush oat in eaormoas volume^ 
fisr day% wedcs, or years continuously, and are 
even dis^igaged from lava during its consolida- 
iixm. When the materials of granite, therefore, 
came in oontact vniA. the (ossilileraus stratum in the 
boivdb of die earth under great pressure, the con* 
taiaed gaeses might be unaUe to escape; yet wh^ 
brought into contact withrodcs, might pass through 
their pores wbh greater fiicility than water is known 
to do. (see p. 74.) These aeriform fluids, such as 
sulphuretted hydrogen, mnrixticacid, and carbonic 
add, issue in maiiy places from rents iniocks, which 
they have dbsoolouredand corroded, softeningsome 
and hardening others. If tke rocks are chained 
with water, they would pass through more readily ; 
for, according to the experiments c^ Henry, water, 
under an hydrostatic pressure of nmety-six feet^ 
will absorb three times as much carbonic acid gas 
as it can under the ordinary pressure of the atmo- 
sphere. Althoi^h this increased power of absorp- 
tion would be diminished, in eonsequence of the 
higher temperature found to exist as we descend 
in the earth, yet Professor Bischoff has shown that 
the heat by no means au^ents in such a propor* 

M 4 



248 B0CK8 ALTESeD ST [Itati 

tion as to counteract the effect of siigm«ile!l jans* 
sure,* There are other gafies, as w^U4Mfthe«sP!» 
bonic acid, which water absorbs, and more rapidly 
in proportion to the amount of pressure. TSow 
even the most compact rocks may be regarded^ 
before they have been exposed to the air and 
dried, in the light of spoi^es filled with water; 
and it is conceivable that heated gases brought 
into contact with them, at great depths, may be 
absorbed readily, and transfiised through their 
pores. Although the gaseous mattec first absoibed 
would soon be condensed, and part with its heat, 
yet the continued arrival of freah supplies from 
below, might, in the course of ages, cause the 
temperature of the water, and with it that of the 
containing rock, to be materially raised. 

M. Foumet, in his description of the metalli- 
ferous gneiss near Clermont, in Auvergne, states 
that all the minute fissures of the rock are quite 
saturated with fi*ee carbonic acid gas, which rises 
plentifully fi*om the soil there and in many parts 
of the surrounding country. The various elements 
of the gneiss, with the exception of the quartz, 
are all softened; and new combinations of the 
acid, with lime, iron, and manganese, are con« 
tuiually in progress, f 

Another illustration of the power of subterra- 

* PoggendorTs Annalen, No. XVI. Second Series, yoLiiL 
f See PiJQciples, Index, '* Auvergne^" &c. 



Ch.XtJ} SUBTERRANEAN OASES. 249 

loiean. gases is afforded by the stufas of St'Csflo^ 
^gearo, situated in the largest of the Lipari Islands; 
Here, according to the description lately published 
by Hoffinann, horizontal strata of tuff, extending 
for four miles along the coast, and forming clif& 
more than 200 feet high^ have been discoloured 
in Tarious places, and strangely altered by the 
^ all-penetrating vapours," Dark clays have be- 
come yellow, or often snow-white; or have assumed 
a 'Aeqtier^ and brecciated appearance, being 
crossed with ferruginous red stripes. In some 
places the fumeroles have been found by analysis 
to consist partly of sublimations of oxide* of iron; 
but it also appears that veins of calcedony and 
opal, and others of fibrous gypsum, have resulted 
from these volcanic exhalations. * 

The reader may also refer to M. Virlet^s ac* 
count of the corrosion of hard, flinty, and jaspi- 
deous rocks near Corinth, by the prolonged agency 
of subterranean gases f; and to Dr. Daubeny's de- 
scription of the decomposition of trachytic rocks 
in the Solfatara, near Naples, by sulphuretted 
hydrogen and muriatic acid gases4 : 

Although in all these instances we can only 
study the phenomena as exhibitied at the surface, 

* Hoffmann's LipiUrischen Inseln, p. 38. Leipzig, 1832, 
f . See Princ. of Qeol, ; and Bulletin de la Soc. Geol. de 
France, tom.ii. p. 330. 
t See Princ. of Geol. ; and Daubeny's Volcanos, p. I67, 

M 5 



250 oBjLGiK car VfVil 

H id eiear that the gaseous flidds miMft bave laade 
iheir inay throu^ llie whole thickness of poir^QS 
or fissured rocks, which iBtervene l)etween ijbe 
sufataranean reservoirs of gas and the esl^etiial 
air. The extent, therefore, of die earth's ervnt^ 
whidii ilie vapours have permeated and are now 
permeating, may be thousands of fittfamns in tluck<^ 
iiess, and their heating andmodifying influence maj 
be spread throughout the whole of this solid oiflas* 
The ^.bove observations are calculated to meet 
some of the objections whidi have been m^ed 
against the metamorphic theory on the ground of 
the small power of rocks to conduct heat; for it 
is well known that rocks, when dry and in the air, 
differ remarkably from metals in this respect. It 
has been asked how the changes which extend 
merely for a few feet from the eontact of a dike 
could have penetrated through mountain masses 
of crystalline strata several miles in thickness^ 
Now it has been stated that the plutonic influence 
of the syenite of Norway, has sometimes altered 
fossiliferous strat£^ for a distance of a quarter of a 
nule, both in the direction of their dip and of their 
•trike. (See Fig. 126. p. 243.) This is undoubtedly 
an extreme case; but is it not far more philoso^ 
phical to suppose that this influence may, under 
favourable circumstances, afieet denser masses, than 
to invent an entirely new cause to account for 
effects merely differing in quantity, and not in 



GtuXIJ METAMdRPHIC STRUCTURE. 251 

kind ? . Tlie'metataiorpl&c th^ry does not require 
lUkta a^lrm thai m>m^ c^tiguouB mass of granite 
bius be^Ok ^e altering power; but merely tl^at an 
acliw» esdstiag in the interior of the earth at an 
unknown, dqpth, whether thermal, electrical^ or 
<ithfer« analogous to that exerted near intruding 
masses of gsanite^ has, in the course of vast and 
mdd&aU^ periods, and when rising perhaps (rom. a 
laxge heated surface^ reduced strata thousands of 
yards thick to a state of semi*fusion, so that on 
oooling they have become crystalline, like gneiss. 
Granite may have been another result of the same 
acti(m in a hi^er state of intensity, by which a 
thorough fusion has been produced ; and in this 
manzier the passage from granite into gneiss may 
be escplained. 

Some geologists are of opinion, that the alter- 
nate layers of mica and quartz, or mica and fel- 
spar, or lime and felspar, are so much more distinct 
in certain metamorphic rocks^ than the ingredients 
composing alternate layers in many sedimentary 
deposits, that the similar particles must be sup- 
posed to have exerted a molecular attraction for 
each other, and to have thus congregated together 
m layers, more distinct in mineral compo^tion 
than before they were crystallized. 

In considering, then, the various data already 
enumerated, the forms of stratification in metar 
morphic rocks, their passage on the one hand 

H 6 



25fl OBIOIK OF IVuth 

mto tbe fosfijliferous^^ and on tlie other into the 
pliitonic formations, and the coaverEBons which 
can b^ ascertained to hare occurred in the vicinity 
oP granite^ ire may conchide that gneiss and mica- 
sehist may be nothing more than altered mica* 
6eous and argillaceous sandstones, that granular 
quartz may have been derived from siliceous sand* 
stone, and compact quartz from the same mate* 
rials. CtayHslatemaybealt^ed shale, and granukr 
marble may have originated in the form of ordi^ 
nary iitaiestoiie, replete witli shells and onrals, which 
have since been obliterated ; and, lastly, calcareous 
sands and marls may have been changed into im- 
pure crystalline limestones. ' 
Homblendenschist," says Dr. MacCuUoch, 
may at first have been mere clay; for clay or 
shale is found altered by trap into Lydian stone, 
a substance differing from hornblende-schist almost 
solely in compactness and uniformity of texture." * 
^^ In Shetland,^' reinarks the same author, ^^ argil- 
laceous-schist (or clay-slate), when in contact with 
granite, is sometimes converted into hornblende- 
schist, the schist becoming first siliceous, and ulti- 
mately, at the contact, hornblende-schist" f 

The andiracite found associated with hypogene 
rocks may have been coal; for we know that, in 
the vicinity of some trap dikes, coal is coiiv^HNied 
into anthracite. 

* Syet, of Geol., vol. L p. 210. f Ibid., p. 211. 



t6 
it 



Ch.XL3 MSTAXOBFHIC ROCKa ^^ 

The total absence of any trace of fosaUs rbfVI 
inclined many gedc^td to attributie the origui.of 
crystalline strata to a period antecedent ta j^iq 
existence of organic beings* Admitting, they 6a}b 
the obliteration, in some cases, of fossils by plulpnic 
action, we might still expect that tracer of th^o^ 
would oftraner occm: in certain, ancient systems -f^ 
slate,' in which, as in Cmnberlandf som^ CQBg]k^* 
marstes occur. But in urging this argumenl9..it 
seems to have been forgotten, that there are str% 
tified formations of enormous thickness, wd of 
various ages, and some of them very modesrn,,^ 
formed after the earth had become the abode of 
living creatures, which are neverth^esis m per|^ 
districts entirely destitute of all vestiges.. of* or- 
ganic bodies. In some, die traces of fossils 
may have been eiFaced by water and acids^ at 
many successive periods; and it is cfear,. that th^ 
older die stratum, the greater is the chance of its 
being non-fossiliferous, even if it has eac^pe^ ^all 
metamoFphic action. *^ >- 

It has been also objected to the metamorphic 
theoiy, that the chemical composition of the se- 
condary strata differs essentially from that of the 
cryjstalline schists, into which they are supposed to 
be convertible. * The " primary '' schists, it is 
said, usually contain a considerable proportion of 

• Dr. Boase, Primary Geology, p. 319. 



potadt w ^todoy «Udk the fiecxindny d^ 
and slates do not, lliese last being the revolt <if ifce 
decoBipositk»i of febpaddc rod^ Spom. wiu^ the 
aUcalinift matter has been abstracted doling die 
prooesBof decompositioo. Bi^ this srea^oning po^ 
eeeds oa insofficaeat anda^^iagaatly wiftUikendai^; 
iar a lai^ p<Htion of -what is nsnaliy cadied day, 
marl, shale, and siate does actually enntain a e^- 
tarn and oftm a considerable proportion of allcali ; 
so that it is difficolt in many ocmnliieB to obtain 
clay or ahale snflkiently fines Saom alkaljbe ing^ 
dients to allow of their being burnt into bcidks or 
used for potteiy. 

Thus the «rgiUaeeous fihalfls, as tbey are. called, 
nad slates of the old red sanditone, in For&rshire 
and other parts of Scotland, are so nnich chai;ged 
with alkali, deriyed firom triturated fehspar« th^^ 
instead of hardening when exposed to fire, thiqr 
mek readily into a glass. They oontain no lime^ 
but appear to consist of ext|:«niely minute grains 
of the various ingredients of granite, which are 
distinctly TisiUe in the eoazser-grained varieties, 
and in almost all the interpcnedsandstooes. These 
laminated days, marls, and shales might, certiunly? 
if crystallized, resemble in cQixi|>osition many of 
the primary strata- 

There is also potash in the regetable lemains 
included in strata, and soda in the salts by which 



Ch.XI.] METAMOmpfilC THEORY. 255 

they are sometimes so largely impregnated, as in 
Patagonia. 

Another objection has been derived from the 
alternation of highly crystalline strata with others 
having a less crystalline texture. The heat, it is 
said, in its ascent from bdiow, must have traversed 
the less altered schists before it reached a higher 
and more crystalline bed. In answer to this, it 
may be observed, that if a number of strata differ- 
ing greatly in composition from each other be sub- 
jected to equal quantities of heat, there is every 
probability that some will be more frisible than 
others. Some, for example, will contain soda, 
potash, lime, or some other ingredient capable of 
acting as a flux; while others may be destitute of 
the same elements, and so r^actory as to be very 
slightly affected by a degree of heat capable of 
reducing others to semi-fiision. Nor should it be 
forgotten that, as a general rule, the less crystal- 
line rocks do really occur in the upper, and the 
more crystalline in the lower part of eadi metar 
morpbic series. 

But it will be impossible for the read^ duly to 
appreciate the propriety of the term metamorphie, 
as applied to the strata hitherto called primcuy, 
until I have shown in the second part of thi^ 
work, ihat these crystalline strata have been formed 
at a great variety of dbtinct periods. 



256 



PART II. 
CHAPTER XII. 

on THB DIFFBRBKT A6BS OP THE FOUR 6RBAT CLASSES 

OF ROCKS. 

Jkqaeoas, phitonic, volcanic, and metamorphic rocks, con- 
sidered chronologicallj — Lehman's division into primitive 
and secondary — Werner's addition of a transition class — 
Neptunian theory — Hutton on igneous origin of granite — 
How the name of primary was still retained for granite — 
The term ** transition," why faulty — The adherence to 
the old chronological nomenclature retarded the progress 
of geology — New hypothesb invented to reconcile the 
Igneous origin of granite to the notion of its high anti- 
quity — Explanation of the chronological nomenclature 
adopted in this work, so far as regards primary, secondary, 
and tertiary periods. 

In the first part of this work the four great classes 
of rocks, the aqueous, the volcanic, the plutonic 
and the metamorphic, have been considered with 
reference to their external characters, their mi- 
neral composition, and mode of origin ; and it now 
remains to treat of the same classes with reference 
to the (UiFerent periods at which they were formed. 
In speaking of the aqueous rocks, for example, it 
has been shown that they are stratified, that some 
are calcareous, others argillaceous, some made up 



Ch. XII.] A0£ OF BOCKS. 257 

of sand, others of pebbles ; that some contain fresh- 
water, others marine fossils, and so forth ; but the 
student has still to learn which rocks, exhibiting 
some or all of these characters, have originated at 
one period of the earth's history, and which at 
another. 

So in regard to the volcanic and ]^ut<Hiii$ iarmy 
ations, we have hitherto examined their mineral 
peculiarities, forms, and mode of origin, but have 
still to inquire into their chronological history. . 
. Lastly, a more carious question will demaiMl 
our attention, wheii we endeavour to ascertain the 
relative ages of the metamorphic rocks, the chro- 
nology of which may be said to be twofold, each 
formation having been deposited at one period, 
and having assumed a crystalline textiure at an^ 
other. 

It was for many years a received opinion, that 
the formation of whole classes of rocks, such as 
the plutonic ■ and metamorphic, began and ended 
before any members of the aqueous and volcanic 
ordersi were produced ; and aldiough this idea has 
long been modified, and is nearly exploded, it 
will be necessary to give some account of the an- 
cient doctrine, in order that beginners may under- 
stand whence part of the nomenclature of geology 
still partially in use was derived. 

About the middle of the last century, Lehman, 
a German miner, proposed to divide rocks into 



LEHMAir AMD WBftNER*S * t^nitL 

dsee cfaeses, llie finst and oldest to be caUedftii- 
mitivtt, annprisiiig die pkiloiiic and metomeiffiiie 
looks'; ike next to be tenned secondftiy, oom^ 
prefaending the mqneous or fiMsililerous «tiiiika^ 
and the remainder or tbird cksB, ^be wtppomi 
eflEect of ^' local floods, and the deluge of. N^iah,'' 
eorresponding to our aUbnrkun, aneient and mo- 
tkem. In the prinutive -clasB, be said, sudi m 
granite and gneiss, tbei«e are no organic remaiiiSy 
nor any .igns of materials derwed from Ae ruiiB 
of pce*€XiBting rooks. Hieu* origin, therefore, 
may have been purdy chonical, antecedent to tbe 
creation of Irring beings, and probably coeval 
wiib the birth of the world itselE The secondary 
formations, on ibe contrary, which ofltea ccmtain 
sand, pebbles, and organie r^nams, nuxst have 
been mechanical deposits, produced after the 
planet bad become the habitation of animals and 
plants. This bold generalieation, although anti- 
cipated in scmie measure by Stenp^ a oentuiy 
b^re, in Italy, formed at the time an imfM>itaiit 
step in the progress of geology, and sketched out 
eorreotly some of the leading divisions into whidi 
rocks may be separated. About half a oentoty 
later, Werner, so justly celebrated for his improved 
miediods of daecriminating the mineralogical cha- 
racters of rocks, aittempted to ioipro¥e Lehman's 
dasaifieation, «»d wiib ihk ^i«w antercaJAted a 
class, called by him " the transitkHi ^ "^ — ** 



Ch.XIL] CLA8BIFICATI0N OP MCKa ^QS^ 

beiw^en the pranitive and seeondaiy. Between 
diese l«st he JmuI 4luo<MF^«d, in BR^tbsm Gov 
many, a series of errata, whidi in their mineral 
pecalmritnes vreve of an intemiediate character, 
partakkig in some degree of diecrystidMne nature 
of micaceous and clay-slate, and yet exhibiting 
here and there ^gns of a mechanical ori^ and 
organic remains* For this group, dierefore, lbnn<- 
ing a passage between Lehman's pximitive and 
secondary rocks, the name of transition was pro- 
posed. They consisted principally of clay^slate 
and an argillaceous sandstone, called greywackS, 
and partly of calcareous beds. It happened in 
the district which Werner first investigated, dutt 
both the primitive and transitioii strata were 
highly inclined, while the beds of the newer and 
fossiliferous rodcs were horisontal. To these hit« 
ter, therefore, he gave the name vA jt&tz^ or fiat; 
and every deposit more moden than the chalk, 
or uppermost of the fiotz series, was designated 
«< &e overflowed land,'' an expression which may 
be regarded as equivalent to alluvium* As the 
followers of Werner soon discovered that the in- 
dined position of the ^ transition beds," and the 
horuEontality of the flikz, or newer fossiliferous 
stxvita, were mere local accidents, lliey soon aban- 
doned the t^rm fiotz; and the ibur dtruioos of the 
Wemerian school were then named primitive, 
transition, secondary, and alluvium. 



KCrrUKlAK TBBOKT. C^MIE 



.. Afflxitfa&tri^qieaiiro^%alflioi^llidrigii6aiii^ 
origin Ind been already demoBstni^^ 
fioDtia, Faunas, and others, and especiaHy by De&- 
tamoBst^ they were all r^aided by Warner '«8 
aipiems, and as mere snbcMrdinate members of the 
secondary formations. * 

. Tills theory of Werner's was eiAed the ^ Nep- 
tmnan," and for many years enjoyed mueh poptH 
lari^* It assumed that the globe had been at 
first invested by an imiversal chaotic ocean^ hold- 
ing die materials of all rocks in sohitiori. Frbm 
die waters of this ocean, granite, gneiss, and other 
crystalline formations, were fii^ precipitated ; 
and afterwards, when the waters were purged of 
these ingredients, and more nearly resembled 
those of our actual seas, the transition strata'were 
deposited. These were of a mixed character, not 
pteely chemical, because the waves and currents 
had already b^un to wear down solid land, and 
to give rise to pebbles, sand, and mud ; nor en- 
tirely without fossils, because a few of the first 
marine animals had begun to exist.' After this 
period, the secondary formations were accumulated 
in waters res^bling those of the present ocean, 
except at certain intervals, when, fi^om causes 
wholly unexplained, a partial recurrence of the 
*^ chaotic fluid'' took place, during which various 

* See FrincipleSy vol. i. chap. iv. 



Ch.XIIJ HUTTON ON GRANITE. flOf 

trap.Tocks^ some highly crystalline^ were fomftecL 
This arbitrary hypothesis rejected all intervention 
of igneous agency, yolcanos being regarded an 
partial and superficial accidents, of trifling aceonnt 
among the great causes which have modified the 
external structure of the globe. 

Meanwhile Hutton, a contemporary of Werner, 
began to teach, in Scotland, that grajoite as well 
as trap was of igneous origin, and had at variofiid 
periods intruded itself in a fluid state into di& 
ferent parts of the earth's crust. He recognized 
and faithfully described many of the phenomena 
of granitic veins, and the alterations produced by 
them on the invaded strata, which have been 
treated of in the ninth chapter. He, moreover, 
advanced the opinion, that the crystalline strata 
called primitive had not been precipitated from a 
primaeval ocean, but were sedimentary strata al- 
tered by heat. In his writings, therefore, and iii 
those of his illustrator, Flayfair, we find the germ 
of that metamorphic theory which has been alr^acty 
expounded.* i 

At length, after much controversy, the doctriiie 
of the igneous origin of trap and granite made 
their way into general favour; but although it 
was, in consequence, admitted that both granite 
and trap had been produced at many successive 

* See chapters X. and XI. 



302 TSaM TRAMSIVION, f^iatlh 

pieri6d% tbe term pidmtive or funsBscry s^.c^mr- 
turned to be applied to the ovystaQiiie fermatidtis 
in genei»l) whether stiBtified, like g^eisS). or ua*^ 
stratifiedst U^e granite^ The pupil wa& told.that 
gnaittte wa& a primary* lock^ bat that somegimr 
rntes were new^ than c^rtaia secondary forrn^ 
ataons; ami in eonformity with the spirit of the 
aeei^at huiguage^ to whieh the teaeher was still: 
detennined to adhere^ a desire was natuaeally en«- 
gendered of extenuating the importance of those 
Biore modern granites which new obsei^ationt 
iwoeffe CQBtinuaUy bringiiig to light. 

A no less decided indinadon was shown to^ 
peesfst in the u^ of the term ^^ transition/' a£ter 
it had been proved to be almost as faulty in its 
original application as that of flotz. The name 
of transition) as already stated^ was first given by 
Werner, to designated a mineral character, inter* 
mediate between the metamorphic state and that 
of an ordincory fbssiliferous rock* But the term 
acquired also from the first a chronolc^ical imr 
port, because it had been appropriated to sedi*- 
mentary formations, which, in the Ha]?t2 and 
other parts of Germany, were more ancient than, 
the oldest of the secondary series, and were char 
xacterized by peoiliar fossil zoophytes and shells^ 
When, therefore, geologists^ found in other districts 
stratified rocks occupying the same position, and 
inclosing similar fossUs, they gave to them also 



the name o£ irami^ni accordiiig to rales which 
will be €sq>laiiied in the next chapter; yet, in 
maay easesf such rocks w^re found not to exhibit 
the same mineral t^tmre which Werner had called 
tiamsition^ On the contrary, many of them were 
not more crystalline than diflEer^at members of the 
ai^eondajEy da^; while, on the other hand, them 
last were sometimes found to assume asemircrysK 
talline and almost metamorphic aspect, and tfaias» 
on lithological grounds, to deserve equally the 
name of transition. So. remarkably wa& diis the 
case in the Swi^ Alps, that certain rocks, which 
had for years been regarded by some of the most 
skilful disciples of Werner to be transition,, were 
at last acknowledged, when their relative position 
and fossils were better understood, to belong to the 
newest of the secondary groups ! If under such cir- 
cumstances the name of transition was retained, it 
is dear that it ought to have been applied without 
reference to the age of strata^ and simply as ex* 
pressive of a mineral peculiarity.. The continued 
appropriation of the term to formations of a given 
date,, induced geologists to go on believing that 
the ancient strata so designated bore a less re- 
semblance to the secondary than is really the case, 
and to imagine that these last never pass, as they 
frequently do, into metamorphic rocks. 

The poet Waller, when lamenting over the 
antiquated style of Chaucer, complains that — 



264 NEPTUNIAN THEORY OF [PaitlL 

We write in sand^ our language grows. 
And, like the tide, our work o'erflows ; 

But the reverse is true in geology; for here it is 
our work which continually outgrows the lan- 
guage. The tide of observation advances witb 
such speed, that improvements in theory outrun 
the changes of nomenclature ; and the attempt to 
inculcate new truths by words invented to express 
a difierent or opposite opinion, tends constantly, 
by the force of association, to perpetuate error; so 
that dogmas renounced by the reason still retain 
a strong hold upon the imagination. 

In order to reconcile'the old chronological views 
with the new doctrine of the igneous origin of 
granite, the following hypothesis was substituted 
for that of the Neptunists. Instead of beginning 
with an aqueous menstruum or chaotic fluid, the 
materials of the present crust of the earth were 
supposed to have been at first in a state of igneous 
fusion, until part of the heat having been diffused 
into surrounding spaced the surface of the fluid 
consolidated, and formed a crust of granite. This 
covering of crystalline stone, which afterwards 
grew tiiiicker and thicker as it cooled, was so hot, 
at first, that no water could exist upon it; but as 
the refrigeration proceeded, the aqueous vapour 
in the atmosphere was condensed, and, falling in 
rain, gave rise to the first thermal ocean. So high 
was the temperature of this boiling sea, that no 



Ch. XII.] THE ORIGIN OF GRAKITEL 265 

aquatic beings could inhabit its waters, and its 
deposits were not only devoid of fossils, but, like 
those of some hot springs, were highly crystalline. 
Hence the origin of the primary or crystalline 
strata. 

Afterwards, when the granitic crust had been 
partially broken up, land and mountains began 
to rise above. the waters, and rains and torrents 
ground down rook, so thait sediment was spread 
over the bottom of the seas. Yet the heat still 
remaining in the solid supporting substances was 
sufficient to increase the chemical action exerted 
by the water, although not so intense as to pre- 
vent the introduction and increase of some living 
ISeings. During this state of things some of the 
residuary mineral ingredients of the primaeval 
ocean were precipitated, and formed deposits (the 
transition strata of Werner), half chemical and 
half mechanical, and containing a few fossils. 

By this new theory, which was in part a revival 
of the doctrine of Leibnitz, published in 1680, on 
the igneous origin of the planet, the old ideas 
respecting the priority of all crystalline rocks to 
the creation of organic beings, were still preserved; 
and the notion, that Jall the semi-crystalline and 
partially fossiliferous rocks belonged to one period, 
while all the earthy and uncrystalline formations 
originated at a subsequent epoch, was also per-< 
petuated. 

N 



266 SIMULTANEOUS ORIOIK 07 [TartIL 

It may or may not be true, as the great Liebnitz 
imagined, that the whole planet was once in a state 
of lique&ction by heat ; bat there are certainly no 
geological proofs that the granite which constitutes 
the foundation of so much of the earth's crust was 
ever in a state of universal fiision. On the con- 
trary, all our evidence tends to show that the form- 
ation of granite, like the deposition of the stratified 
rocks, has been successive, and that different por^ 
tions of granite have been in a melted state at 
distinct and often distant periods. One mass was 
solid, and had been firactured, before another body 
of granitic matter was injected into it, or through 
it, in the form of veins. In short, the universal 
fluidity of the crystalline foundations of the earth's 
crust, can only be imderstood in the same sense 
as the universality of the ancient ocean. All the 
land has been under water, but not all at one 
time ; so all the subtexranean unstratified rocks to 
which man can obtain access have been melted, 
but not simultaneously. 

In the present work the four great classes of 
rocks, the aqueous, plutonic, volcanic, and meta- 
morphic, will form four parallel, or nearly parallel, 
columns in one chronological table. They will be 
considered as four sets of monuments relating to 
four contemporaneous, or nearly contemiporaneous, 
series of events. I have endeavoured, in the Frontis- 
piece, to express the manner in which members of 



Cta.XII] THE FOUR CLASSES OF ROCKS. 267 

each of the four classes may have originated simul- 
taneously at every geological period. According 
to this view, the earth's crust may have been con- 
tinually remodelled, above and below, by aqueous 
and igneous causes, from times indefinitely remote. 
In the same manner as aqueous and fossiliferous 
strata are now formed in certain seas or lakes, 
while in other places volcanic rocks break out at 
the surface, and are connected with reservoirs of 
melted matter at vast depths in the bowels of the 
earth, — so, at every era of the past, fossiliferous 
deposits and superficial igneous rocks were in 
progress contemporaneously with others of sub- 
terranean and plutonic origin, and some sedi- 
mentary strata were exposed to heat and made to 
assume a crystalline or metamorphic structiu'e. 

It can by no means be taken for granted, that 
during all these changes the solid crust of the 
earth has be^i increasing in thickness. It has 
been shown, that so far as aqueous action is con- 
cerned, the gain by fresh deposits, and the loss by 
denudation, must at each period have been equal ; 
and in like manner, in the inferior portion of the 
earth's crust, the acquisition of new crystalline 
rocks, at each successive ei^a, may merely have 
counterbalanced the loss sustained by the melting 
of materials previously consolidated. As to the 
relative antiquity of the crystalline foundations of 
the earth's crust, when compared to the fossilifarotis 

N 2 



and volcanic rodks which they support, I hkv^dA 
ready stated, in the first chapter, that to prbnouii^, 
an opinion on this matter is as difficult as at ofi^ 
to decide ^hich of the two, whether the founda^ 
tions or superstructure of an ancient city built'' on 
wooden piles may be the oldest. We have seeii 
that to answer diis question, we must first be pre^ 
pared, to say whether the woric of decay and re^ 
storation had gone on most rapidly above or below, 
whether the average. duration of the piles has ex- 
ceeded that of the stone buildings, or the contrary; 
S9 also in regard to the relative age of the su- 
perior and inferior portions of the earth's crust; 
we cannot hazard even a conjecture' on this point, 
until we know whether, upon an average, the power 
of water, above, or that of fire below, is most effi- 
cacious in giving new forms to solid matter. 

After the observations which have now been 
made, the reader will perceive that the term pri- 
marj'^ must either be entirely renounced, or, if re- 
tained, must be difierently defined, and not made 
to designate a set of crystalline rocks, some of 
which may^ be newer than the secondary form* 
ations. In this work I shall follow most nearly 
the method proposed by Mr. Boue, who has called 
all fossiliferous rocks older than the secondary by 
the, name of prunary, which thus becomes a sub- 
stitute for the term transition, so far as regards 
the aqueous strata. To prevent confusion, how- 



Ch. XU.2 OF THE FOUR CLASSES. OF ROCKS. 269 

ever, I shall always speak' of these as ^e primary 
fassilifer.ous formations, because the word primary 
has hitherto been almost inseparably connected 
with the idea of a non-fossiliferous rock. 

If we can prove any plutonic, volcanic, or meta- 
morphic rocks to be older than the secondary 
formations, such rocks wiU also be primaiy, ac- 
cording to this system. Mr. Bou6 having with 
great propriety .excluded the metamorphic rocks, 
da a classyirom the primary formations, proposed 
to call them all « crystalline schists," restricting 
the name of primary to the older fossiliferous or 
transition strata. 

. As there are secondary fosfiiliferous strata, so 
we shall find that there are plutonic, volcanic, 
and metamorphic rocks of contemporaneous origin, 
which I shall also term secondary. 

In the next chapter it will be shown that the 
strata above the chalk have been called tertiary. 
I^ therefore, we discover any volcanic, plutonic, 
or metamorphic rocks, which have originated since 
the deposition of the chalk, these also will rank as 
tertiary formations. 

It may perhaps be suggested that some meta- 
morphic strata, and some granites, may be anterior 
in date to the oldest of the primary fossiliferous 
rocks* The opinion is certainly not improbable, 
and will be discussed in future chapters; but I 
lOay here observe, that when we arrange the four 

N 3 



270 ^6ES OF ROCKa [Partli. 

classes of rocks in four parallel columns in one 
table of chronology, it is by no means assumed 
that these columns are all of equal length; <me 
may begin at an earlier period than the rest, and 
another may come down to a later point of time. 
In the small part of the globe hitherto examined, 
it is hardly to be expected that we should have 
discovered either the oldest or the newest of all 
the four classes of rocks. Thus, if there be pri- 
mary, secondary, and tertiary rocks of the fossili- 
ferous class, and in like manner primary, second* 
ary, and tertiary plutonic formations, we may not 
be yet acquainted with the most ancient of the 
primary fossiliferous foeds» or with the newest of 
the plutonic, and so of the rest 



271 



CHAPTER XIII. 

ON THE DIFFERENT AGES OF THE AQUEOUS ROCKS. 

On the three principal tests of relative age — superposition^ 
mineral character, and fossils — Change of mineral cha» 
racter and fossils in the same continuous formation^ 
Proo& that distinct species of animals and plants have 
lived at successive periods — Test of age by included 
fragments — Frequent absence of strata of intervening 
periods — Principal groups of strata in western Europe 
— Tertiary strata separable into four groups, the fossil 
shells of which approach nearer to those now living in 
proportion as the formation is more modern — Terms 
Eocene, Miocene, and Pliocene — Identifications of fossil 
and recent shells by M. Deshayes — Opinions of Dr. Beck. 

In the last chapter I spoke generally of the chro- 
nological relations of the four great classes of 
rocks, and I shall now treat of the aqueous rocks 
in particular, or of the successive periods at which 
the different fossiliferous formations have been 
deposited. 

Now there are three principal tests by which 
we determine the age of a given set of strata; 
first, superposition; secondly, mineral character; 
and, thirdly, organic remains. Some aid can oc- 
casionally be derived from a fourtli kind of proo^ 
namely, the &ct of one deposit including in it 

N 4 



272 TESTS OF THE DIFFERENT AGES [P»rt II. 

fragments of a preexisting rock, which last may 
thufi be shown, even in the absence oi all other 
evidence, to be the older of the two. 

SuperposUiinu \ — The first and principal test of 
the age of one aqueous deposit, as compared to 
another, is relative position. It has beeiT already 
stated, that where the strata are horizontal, the 
bed which lies uppermost is the newest of the 
whole, and that which lies at die bottom the most 
andent. So, of a series of sedimentaiy formations, 
they are like voliunes of history, in which each 
writer has recorded the annals of his own times, 
and then laid down the book, with the last written 
page uppermost, upon the volume in which the events 
of the era immediately preceding were comme- 
morated. In this manner a lofty, pile of chronicles 
is at length accumulated ; and they are so arranged 
as to indicate, by their position alone^ the order in 
which the events recorded in them have occurred.' 

In regard 'to the crust of the earth, however, 
there are some regions where, as the student has 
already been informed, the beds have been dis- 
turbed, and sometimes reversed. (See pp. 118, 
114.) But the experienced geologist will not be 
deceived by these exceptional cases. When he 
finds that the strata are fractured, curved, in- 
clined, or vertical, he knows that the original 
order of superposition must be doubtful, and he 
will endeavour to find sections in some neighbour- 



Ch.XIlL] «- • rOF'JKOtJBOWi' ROCKS. "' '27^ 

i^g'« district wheri^ the B^uta'dre horizontal, or 
mly slightly kidinecL Here^ it is impossible that 
they can have been extensivdy thrown over and 
turned upside down, for such a derangement can- 
not have taken place throughout a wide area with- 
out leaving manifest signs of displacement and 
dislocation. 

, . Mineral eharader. — The same rocks may often 
be observed to retain for miles, or even hundreds 
of miles, the same mineral peculiarities, if we fol- 
low them in the direction of the planes of stratifi- 
cation. But this uniformity ceases almost imme- 
diately, if we pursue them in an opposite direction. 
In that case we can scarcely ever penetrate a 
stratified mass for a few himdred yards, much 
less several miles, without beholding a succession 
of extremely dissimilar calcareous, argillaceous^ a^d 
siliceous rocks. . These phenomena lead to the 
conclusion, that rivers and currents have dispersed 
the same sediment over wide areas at one period, 
but at successive periods have been charged, in the 
same r^on, with very different kinds of matter. 
The first observers were so astonished at the vast 
spaces. over which they were able to follow the 
same homogeneous rocks in a horizontal direction, 
that they came hastily to the opinion, that th^ 
whole globe had been environed by a succession 
of distinct aqueous formations, disposed round the 
nucleus of the planet, like the concentric coats of 

N 5 



274 TESTS OF THE DIFFERENT AOES t^artlL 

an onion. But although, in &ct, some formations 
may be continuous over districts as large as half 
of Europe, or even more, yet most of them either 
terminate wholly within narrower limits, or soon 
change their lithological character. Sometimes 
they thin out gradually, as if the supply of sedi- 
ment had failed in that direction, or they come 
abruptiy to an end, as if we had arrived at tiie 
borders of the ancient sea or lake which served 
as their receptacle. It no less frequentiy happens 
that they vary in mineral aspect and composition, 
as we pursue tiiem horizontally. For example, 
we trace a limestone for a hundred miles, until it 
becomes more arenaceous, and finally passes into 
sand, or sandstone. * We may tiien follow tiiis 
sandstone, already proved by its continuity to be 
of the same age, tiiroughout another district a 
hundred miles or more in length. 

Organic remains, — This character must be used 
as a criterion of the age of a formation, or of the 
contemporaneous origin of two deposits in distant 
places, under very much tiie same restrictions as 
the test of mineral composition. 

First, the same fossils may be traced over wide 
regions, if we examine strata in the direction of 
tiieir planes, although by no means for indefinite 
distances. This might have been expected; for 
although many species of animals and plants have 
a wide geographical range, yet each species ge« 



Ch. XIIL] OF AQUEOUS ROCK& 275 

nerally inhabits a small part only of the entire 
globe, and is often incapable of existing in other 
regions. But, in those cases where the fossils vary, 
the mineral character of the rock often remains 
constant; and, on the other hand, the fossils are 
sometimes uniform throughout spaces where the 
lithological nature of the rock is variable. In this 
manner we are jfrequently enabled to prove the 
contemporaneous origin of the same formation by 
one test, when the other fails. 

Secondly, while the same fossils prevail in a 
particular set of strata for hundreds of miles in a 
horizontal direction, we seldom meet with the 
same remains for many fathoms, and scarcely 
ever for several hundred yards, in a vertical lin^ 
or a line transverse to the strata. This &ct has 
now been verified in almost all parts of the globe, 
and has led to a conviction, that at successive 
periods of the past, the same area of land and 
water has been inhabited by species of animals 
and plants as distinct as those which now people 
the antipodes, or which now coexist in the arctic, 
temperate, and tropical zones. It appears, that 
&om the remotest periods there has been ever a 
coming in of new organic forms, and an extinction 
of those which pre-existed on the earth ; some 
species having endured for a longer, others for a 
shorter time; but none having ever reappeared 
after once dying out. The law which has governed 

N 6 



276 TESTS OF THE DIFFERENT AGES CPWt U. 

the creation and extinction of species iseeins to 
be expressed in the verse of the poet, 

Natura il fece e poi ruppe la stampa. — Ariotto, 
Nature made it, and then broke the die. 

And this circumstance it is, which confers on fos- 
sils their highest value as chronological tests, 
giving to each of them, in the eyes of the geo- 
logist, that authority which belongs to contem- 
porary medals in history. 

The same cannot be said of each peculiar variety 
of rock ; for some of these, as red marl and red 
sandstone, for example, may occur at once at the 
top, bottom, and middle of the entire sedimentary 
series; exhibiting in each position so perfect an 
identity of mineral aspect as to be undistinguisb- 
able. Such exact repetitions, however, of the 
same mixtures of sediment have not often oc- 
curred, at distant periods, in precisely the same 
parts of the globe ; and even where this has hap- 
pened, we may usually avoid confounding together 
the monuments of remote eras, by the aid of fossils 
and relative position* 

Test by included fragments of older rocks, — It 
was stated, that independent proof may sometimes 
be obtained of the relative date of two formations, 
by fragments of an older rock being included in 
a newer one. This evidence may sometimes be 
of great use, where a geologist is at a loss to 



cb.xiii] ^ ' Dr:A<|ir£ot7S'mociB. '-'' IT Q72 

detevndbe iJie r^latire'cige of two^fennadME^ ^fimb 
want of clear sections exMbhing dteirtme ordst' 
of position, or because the strata of each group 
are vertical. In such cases we sometime dis- 
cover that the more modem rock has been in part 
derived^firom die degradation of the older. Thus^ 
for example, we may find chalk witii flints; and^ 
in another part of tiie same country, a distinot 
series, consisting of alternations of day, sand, and 
pebbles. If some of tiiese pebbles consist of flints^ 
widi fbssil shells of the same species as those in 
tiie dialk, we may confidentiy infer tiiat the chalk 
is the oldest of tiie two formations. 

The number of groups into which the fossili- 
ferous strata may be separated, are more or less 
numerous, according to tiie views of classification 
which different geologists entertain; but when we 
have adopted a certain system of arrangement, we 
immediately find that a few only of tiie entire 
series of groups occur one upon the other in any 
single section or district. 

The thinning out of individual strata was before 
described (p. 37.). But let tiie annexed diagram 

Fig. 127. 



1278 CHRONOLOGICAL CLASSIFICATION CFwrtlL 

rejNresent seven fossiliferous groups, mstead of as 
many strata. It will then be seen that in the middle 
all the superimposed formations are present ; but 
in consequence of some of them thinning out, No. 2. 
and No. 5. are absent at one extremity of the sec- 
:don, and No. 4. at the other. 

If the reader consults the Frontispiece, he will 
see, that as the strata A rest unconformably upon 
the older groups, a, b, c, ejfi g^ we should meet 
with a very different succession in a vertical seo- 
tion exposed at different places; in one spot A 
lying immediately on c, in another on y, and so 
forth. Now here the difference has been partly 
occasioned by denudation ; the formations a, 5, for 
instance, once extended much fiurther to the 
left, and but for denudation would have been 
everywhere interposed between A and the rocks 
e^fi g* In many instances the entire absence of 
one or more formations of intervening periods be- 
tween two groups, such as A and c, (see Frontis^ 
piece,) arises, not from the destruction of what 
once existed, by denudation, but because no strata 
of an intermediate age were ever deposited on c 
They were not formed at that place, either be- 
cause the r^on was dry land during the interval, 
or because it was part of a sea or lake to which 
no sediment was carried. 

In order, therefore, to establish a chronological 



Olxhl] of aqueous rocks. 279 

succession of fossiliferous groups, a geologist must 
begin with a single section, in which several sets 
of strata lie one upon the other. He must then 
trace these formations, by attention to their mineral 
character and fossils, continuously, as &r as pos- 
sible, from the starting point. As often as he 
meets with new groups, he must ascertain by 
superposition their age relatively to those first 
examined, and thus learn how to intercalate them 
in a tabular arrangement of the whole. 

By this means the German, French, and Eng- 
lish geologists have determined the succession of 
strata throughout a great part of Europe, and have 
adopted pretty generaUy the following groups, al- 
most all of which have their representatives in the 
British Islands. 

Groups of FossUiferotu Strata observed in Western 
Europe, arranged in what is termed a descending 
series, or beginning toith the newest 

1. Newer Pliocene. "i 

8. Older Pliocene. I Tertiary or SuprBcretace- 

S. Miocene. t ous.* 

4. Eocene. J 



* For tertiary, Mr. De la Beche has used the terra " supra- 
cretaceous," a name implying that the strata so called are 
superior in position to the chalk. 



280 



CHRONOLOGICAL CLASSIHCATION 



tPttt II. 



5. Chalk. 

6. Grcenfand. 

7. Wealden. 

8. Upper OoUle. 

9. Middle Oolite, 
la Lower Oolite. 

11. Lias. 

1 2. Upper New Red sandstone and 

Muschelkalk. 
IS. Lower New Red and Magne^ 
tdan limestone^ 

14. Coal. 

15. Old Red sandstone. 

16. Upper Silurian. 

17. Lower Silurian. 

18. Cambrian and older fossili- 

ferous strata. 



^Secondary. 



Primary fossiliferous (or 
transition of some au- 
thors). 



A glance at the above table will show that the 
three great sections called primary fossiliferous, 
secondary, and tertiary, are by no means of equi- 
valent importance, if the eighteen subordinate 
groups comprise monuments relating to equal por- 
tions of past time, or of the earth's history. But 
this we cannot assert ; but merely know that they 
each relate to successive periods, during which cer- 
tain animals and plants, for the most part peculiar 
to that era, flourished, and during which different 
kinds of sediment were deposited in the splice noV 
occupied by Europe. 

If we were disposed, on palseontological grounds, 
to divide the entire fossiliferous series into a few 
groups, less numerous than those in the above 



Cb.XIII.] ^ OF AQUEOUS ROGK& 261 

table, and more nearly co-ordinate in value than 
the sections called primary, secondary, and ter* 
tiary, -we might, perhaps, adopt the six following 
groups or periods. * At the same time I may ob- 
serve, that in the present state of the science, when 
we have not yet compared the evidence derivable 
from all classes of fossils, not even those most ge- 
nerally distributed, such as shells, corals, and fish, 
such generalizations are premature, and can only 
be regarded as conjectural. schemes for the found- 
ing of large natural groups. 

{from the Newer Pliocene to the 
Eocene inclusive. 

2. Cretaceous - . f from the Chalk to the Wealden in- 

L elusive. 
S. Oolitic . - - from the Oolite to the Lias inclusive. 

r including the Keuper, Muscbel- 

4. Upper New Red - - i ^^IK and Banter Sandstein of 

L the Germans. 

f including Magnesian Limestone 

5. Lower New Red «id I (2^^,^^^,)^ coal, «id Old Ked 

CriKjmferous - - ]^ „„d,tone. . 

. r from the Upper Silurian to the oldest 

6. Pnmary fossiliferous - -{ ^ mt i. : i • ^ 

^ \ fossiliferous rocks inclusive. 

The limits of this volume will not allow of a 
full description, even of the leading features of all 
the formations enumerated in the above tables; 
but I shall briefly advert to each of them in chro- 

* Palaeontology is the science which treats of fossil re- 
mains, both animal and vegetable. Etym, waKcuog, palahs, 
ancient, ovra^ onia, beings, and Xoyoc, ^os, a discourse. 



282 CLASSIFICATION OF THE CPartll. 

nological order, as they will afford illustrations of 
the rules of classification, the tests of relative age, 
and the mode of deriving information from geolo- 
gical monuments respecting the former history of 
the earth and its inhabitants. 

Tertiary formations. — These strata, as we have 
seen, were so called because, when first discovered, 
they were observed to be of a date posterior to 
th^ chalk, which had long been regarded as the 
last or uppermost of the secondary formations. 
It was remarked, that in France, Italy, Germany, 
and England, the tertiary deposits occupied a posi- 
tion, in reference to all older rocks, like that of the 
waters of lakes, inland seas, and gulfs in relation 
to a continent, being often, like such waters, of 
great depth, though of limited area, and frequently 
occurring in detached and isolated patches. The 
strata were for the most part horizontal, but 
usually surrounded by older rocks, of which the 
beds were highly inclined or vertical. 

On comparing together the fossils of the aqueous 
formations in general, especially the testacea, which 
are the most abundant and best preserved of all, 
it appears that those of the primary fossiliferous 
rocks depart most widely in form and structure 
from the type of the living creation, those of the 
secondary less widely, and the tertiary least of all. 
In like manner, if we divide the tertiary deposits 
into four principal groups, and then compare the 



Ch.XIII.] TEBTURY FORMATIONS. . 283 

fossil shells which they contain with the testacea now 
living in the nearest seas in the same latitudes, we 
find that the shells of the oldest strata have much 
less resemblance, on the whole, to the fauna of the 
neighbouring seas, than those of the newest group. 
In a word, in proportion as the age of a tertiary 
formation is more modern, so also is the resem- 
blance greater of its fossil shells to the testaceous 
&una of the actual seas. 

Having observed the prevalence of this change 
of character in the tertiary strata of France and 
Italy, in 1828, I conceived the idea of classing the 
whole series of tertiary strata into four groups, en- 
deavouring to find characters for each expressive 
of their difiPerent degrees of affinity to the living 
iauna. I hoped that an estimate of this varying 
relation to the fauna of the existing seas might be 
obtained by determining the proportional number 
of shells identical with living species which be- 
longed to each grpup. With this view, I obtained 
information respecting the specific identity of many 
tertiary and recent shells from several Italian na- 
turalists ; and among others, firom Professors Bo- 
nelli, Guidotti, and Costa. 

I have explained at length, in the Principles of 
Geology, the opinions which were at that time 
generally entertained respecting the classification 
of tertiary formations, and the observations which 
led me, in 1828, to divide them into four groups. 



234 CLASSIFICATION OF THE • CP«t H- 



by reference n6t only tx> their geological position^ 
but also to the proportional number of recent 
species found fossil in each. I have also there 
stated, that having, in 1829, become acquainted 
with M. Deshayes, of Parisj I learnt from him 
that he had arrived, by independent researches 
and by the study of a large collection of fossil and 
recent shells, at very similar views. At, my re- 
quest he drew up, in a tabular form, lists of all the 
shells known to him to occur both in some tertiary 
formation and in a living state, for the express 
purpose of ascertaining the proportional number 
of fossil species identical with the recent which 
characterized the successive groups ; and this table 
was published by me in 1833. * The number of 
tertiary fossil shells examined by M. Deshayes 
was about 3000; and the recent species with which 
they had been compared, about 5000. The result 
at which that naturalist arrived >vas, that in the 
oldest tertiary deposits, such as those found near 
London and Paris, there were about 3^ per cent 
of species of fossil shells identical with recent 
species ; in the next, or middle tertiary period, to 
which certain strata on the Loire arid Gironde, in 
France, belonged, about 17 per cent. ; and in the 
deposits of a third, or newer era, embracing those 
of the Subapennine hills, from 35 to 50 per cent 

* See Ptdnc. of Oeol. vol. iii.. 1st ed. 



CI). XIJIJ TESTIARY FORMATIONS.' ^gjl 

In^fprmations still more modern, some of wluQhl 
bad particularly studied in Sicily, where tliey air 
tain a vast thickness and elevation above the sea, 
the number of species identical with those now 
li^ving was jfrom 90 to 95 per cent. For the sake 
of clearness and brevity, I proposed to give short 
technical names to these four groups, or the periods 
tQ .which they respectively belonged. I called the 
firgt or oldest of them Eocene, the second Miocene, 
the third Older Pliocene, and the last or fourth 
Newer Pliocene. The first of the above terms. 
Eocene, is derived from >}a)f, eos, datvn, and xaivo^, 
Cfunos, recent, because the fossil shells of this 
period contain an extremely, small proportion of 
living species, which may be looked upon as indi- 
cating the dawn of the recent or existing state of 
the testaceous faima. 

The other terms, Miocene and Pliocene, arecom- 
parative; the first meaning less recent, (from fttioy, 
melon, less, and xaivof, cainos, recent^) and the 
other more recent, (from vAsiov, pleion, more, and 
xonvfiSy cainos,. r^cen^) they express the more or 
less, near approach which the deposits of these 
eras, whejp contrasted with each other, make to the 
existing creation, at least so far as the moUuscii 
are. concerned. It may assist the memory of stu- 
dents to remind them, that the Jlkfiocene contain a 
inmor proportion, and Pfiocene a comparative pin- 
rjjity of recent species ; and that the greater num- 



2g5 CI.AS8IF1CATIOH OF THE tTrntlL 

ber of recent species always implies the more 
modem origin of the strata. 

Two subjects of discussion have arisen respect- 
ing the tables above alluded to; first, whether the 
fossil shells were, upon the whole^ correctly identi- 
fied with recent species by M. Deshayes ; secondly^ 
whether such a per-centage of recent species oc- 
curring fossil in particular groups, afiPords the best 
criterion for estimating the relation of each fossil 
fiiuna to the living creation. 

Now in r^ard to the per-centage test, its appli- 
cation must evidendy depend on the extent to 
which concholopsts are agreed in their determin- 
ation of species. In every branch of natural his- 
tory there is always some difference of opinion as 
to certain species which are variable in their 
characters, and seem to pass by imperceptible 
gradations into other forms, considered by many 
zoologists and botanists as entitled to rank as dis- 
tinct species. The difficulty of defining the limits 
in such cases is not greater, perhaps, in conchology 
than in other departments; but it happens that 
this science has advanced very rapidly since the 
year 1 830, when M. Deshayes drew up the tables 
published in the Principles of Greology. In that 
year he had it in his power to refer to no more 
than 5000 species of recent shells then in Paris ; 
but the number of species now in the public and 
private collections of Europe has increased to 



Ch.Xinj TERTIARY FORMATIONa 287 

between 8000 and 9000 ; and, what is of no less 
consequence, individuals of species which before 
that time were extremely rare, have been supplied 
in abundance. Fossil shells also have been col- 
lected with equal zeal and success ; and thus the 
facility of discriminating nice distinctions in closely 
allied species, or of deciding which characters are 
constant and which variable, has been greatly pro- 
moted ; and the study of these more ample data 
has led all conchologists to separate many species, 
both of fossil and recent shells, which before they 
had confounded together. 

In consequence of the changes of opinion brought 
about by these additions to our knowledge, it has 
become necessary not only to examine all the 
newly discovered fossil and recent testacea, but 
also to reconsider all the species previously known. 
As this laborious task has not yet been executed 
by M. Deshayes, engaged as he is in other scien- 
tific labours, I am imable at present to offer to 
the reader the improved results which the revi- 
sion of the tables drawn up in 1830 woidd afford. 
In the mean time I have obtained the aid of se- 
veral eminent conchologists, and in particular of 
Dr. Beck, of Copenhagen, in comparing a great 
number of the recent and fossil shells which had 
been identified. By this investigation I have 
come to the conclusion that the per-centage of 
recent species in a fossil state is decidedly less. 



288 CLASSIFICATION OF THE [FMt U. 

especially in the older tertiary strata, than was in- 
dicated in the list published in 1833. A large 
number, in particular, of the forty*two species of 
Eocene testacea, to which the names of recent 
shells were given in the tables, cannot be consi- 
dered as identical, if we adopt the same standard 
of specific distinctions as is recognized in the new 
edition of Lamarck's conchology, ' edited by M. 
Deshayes himself in 1836. 

But although many corrections are indispen- 
sable, and the proportion of recent species found 
fossil in the Eocene, Miocene, and older Pliocene 
strata may be considerably less than was at first 
supposed, we have no reason on this account to 
feel discouraged in an attempt to found the classi- 
fication and nomenclature of the tertiary periods 
on the great principle before explained; namely, 
the comparative resemblance of the testaceous 
fauna of each period to that of the neighbouring 
seas. There can be no cabalistic virtue in such 
numbers as 3. 17. or 40., which were at first 
imagined to express correctly the proportional 
number of identical species in three of the tertiary 
periods ; but until the time arrives when we can 
obtain the general acquiescence of conchologists 
as to the real proportional numbers, we must en- 
deavour to find some readier method of estimat- 
ing the relation of one fiiuna to another; a method 
not involving the question of the identity or non- 



CkXIII.;] TERTIARY FORMATIONS. 289 

identity of every fossil with some known recent 
species. 

Now, it has been suggested by Dr. Beck that, 
in order to form such an estimate of the compara^- 
tive resemblance of the faunas of different eras, we 
mq,y follow the same plan as would enable us to 
appreciate the amount of agreement or discre* 
pancy between the faunas now existing in two 
distinct geographical regions. 

It is well known that, although nearly all the 
spieciefi of moUusca inhabiting the temperate zones 
on each side of the equator are distinct, yet the 
whole assemblage of species in one of these zones 
bears a striking analc^ to that in the other, and 
diifisrs in a corresponding manner from the tro- 
pical and arctic faunas. By what language can 
the zoologist express such points of agreement or 
disagreement, where the species are admitted to 
be distinct? 

. . In auch cases it is necessary to mark the relap- 
tire abundance in the two regions compared of 
certain .fionilies, genera, and sections of genera; 
tlie eDtire absence of some of these, the compara* 
tive strength of others, this strength being some-^ 
times represented by the numbers of species, 
aometames by the great abundance and size of the 
incUvicbi^ of certain species. It is, moreover, im- 
poitaat to estimate the total number of species 
inhabiting a given area; and., also the average 



390 CXA8SIFICATION OF THE Part It 

proporticm of species to genera, as this difiPers ma^ 
terially according to climate. Thus, if we adopt 
comprehensive genera like those of Lamarck, we 
shall find, according to Dr. Beck, that, upon an 
average, there are. in arctic latitudes nearly as 
many genera as species; in the temperate re- 
gions, about three or four species to a genus ^ in 
the tropical, five or six species to a genus. 

The method of which the above sketch conveys 
but a faint outline, is the more easy of application 
to the tertiary deposits of Europe, because the 
conchological fauna of the Eocene period indicates 
a tropical climate ; that of the Miocene strata, a 
climate bordering on the tropics; and that of the 
Older and Newer Pliocene deposits, a climate much 
more closely approaching to, if not the same as^ 
that of the seas in corresponding latitudes. 

Although I cannot enter in this work into 
farther details, it may be stated that, if we com* 
pare tertiary formations on this principle, the no* 
menclature above proposed will not be inappnn 
priatc; for the &una of the older, or Eocene, 
tertiary formations is still the first in the order of 
time in which there is an assemblage of testacea 
like that of the present ocean between the tropics ; 
and in this period a small proportion of moUusca 
are undistinguishable from living species; whereas 
at the opposite extreme of the series, or in the 
Newer Pliocene deposits, all conchologists agree 



Ch. XUI.] TERTIARt FORMATIONS, 291' 

that die marine shells are all, or nearly all^. 
idfodcal with those now inhabiting the nearest 
seaB. As to the Miocene and Older Pliocene 
groups, the terms less and more will always ex- 
press correctly the different degrees of analogy^ 
which their fossils bear to the assemblage of 
living i^cies in similar latitudes. 

But it should never be forgotten that, aa the 
extinct species preponderate in all groups, with 
the exception of the Newer Pliocene, it is from 
their characters that we derive the distinguishing 
feature in the palaeontology of each period. The 
relative approach which the shells may make to 
the living fauna affords a usefid and interesting 
term of comparison ; but it is one feature only, and 
by no means the most prominent one, in the or* 
ganic remains of successive periods. 



o 2 



292 



CHAPTER XIV. 

RXCENT AND TERTIARY FORMATIONS. 



• 



How to distinguish Itecent from Tertiary strata — Recent and 
Newer Pliocene strata near Naples — near Stockholm and 
Chrifltiania — in South America, on coasts of ChiK and 
Peru — Rocks of Recent period, with human skeleton, in 
Ouadak>upe — Shells of living species, with extinct mam- 
malia, in loess of the Rhine — Recent and Newer Pliocene 
deposits in England — Older Pliocene strata in England*- 
Crag -^ Red and Coralline crag — their fosdUs in part dis* 
tinct — their strata unconformable — belong to the saipe 
period — London clay — Its shells and fish imply a tropical 
dimate •— Tertiary mammalia — Fossil quadrumana. > 

RMCEyrr and Newer PHocene strata. — If we b^in 
with the history of the more modem aqueoua form- 
ations, and then pass on to the more ancient, the 
first strata which present themselves are those 
termed, in the last chapter, the Newer Pliocene. 
But in what manner shall we define the limits be* 
tween this group and those fossiliferous deposits 
which are now in progress, or which have accumu- 
lated under water since the globe was inhabited by 
man? The strata last mentioned, namely, those 
of the human period, I shall call Mecent^ distin- 
guishing them fi*bm the most modem tertiary 
formations. Strata may be proved to belong to 
the Recent period by our finding in them the 



I 



I 



Ch.Xiy.3 RECENT STRATA. 293 

bones of man iii a fi:>ssil stat^ that ia to say, im^ 
bedded in them by natural causes; or we -may 
recognize them by their x»Btaining articles febri- 
cated by the hands of man^ or. by showing. that 
siicK deposits did not exist ia tlie place whene we 
now observe them at a given* period of the past 
when man existed^ do that they must be of subset 
quent origin. In general all recent formadonii lie 
hidden from our sight b^ieath liie waters of lakes 
and jseas; but we may examine them wherever 
these lakes or seas have been partially converted 
into land, as in the deltas of rivers, or where the 
submerged ground has been heaved up by sub* 
terranean movement^ and laid dry. 

Thus at Puzzuoli, near Naples, marine strata 
are seen containing fragments of s<^ulptare^ pot- 
tery, and the remains oif buildings, together with 
innumerable Shells retaining in part their colour, 
and of the. same species as those now inhabiting 
the Mediterranean. The uppermost of these beds 
is about twenty feet above the level of the sea» 
Their emergence can be proved to have taken 
place since the banning of the- sixteenth cen* 
tury«* But the hills at the base of which these 
strata have been deposited, and those of the in- 
terior of the ac^acent country round Naples, some 
of which rise to the height of 1500 feet above the 



* See Principles, Index, *' SerapisJ 

o 3 



i9 



. SKCEHT AHD C^^tttlt 

seai are formed of horizontal strata of the N^weif 
I^iocene period; that is to say, die marine fik^ 
observed in them are of living spedes^and^t 
are not accompanied by any sremains of maai ^r 
his works. Had toch been discovered, it wotdd 
have afforded to the antiquary and geologist rmx* 
ter bf great surprise, since it would have diown 
that man was an inhabitant of that. part of the 
globe, while the materials composing the predict 
hills and plains of Campania were still i^ the 
progress of deposition at the bottom of the Ma; 
'vhereas we know that for nearly 3000 years^ or 
from the times of the earliest Greek colonists, ho 
extensive revolution in the physical geography of 
that part of Italy has occurred* 

In Sweden, analogous phenomena have been ob* 
served* Near Stockholm, for example, wh^ii the 
canal of Sodertelje was dug, horizontal beds of 
sand, loam, and marl were passed thrbij^fa, in 
some of which the same peculiar assemblage of 
testacea which now live in the Baltic were found. 
Mingled with these, at different depths, were de- 
tected various works of art implying a rude state 
of civilization, and some vessels built before the 
introduction of iron. These vessels and imple* 
ments must have sunk to the bottom of an arm of 
the sea, afterwards filled up with sand and loam 
including marine shells, and the whole must then 
have been upraised ; so that the upper beds became 



Cli.XlV.3 NEWBR PLIOCBNS STRATA. $05 

,iixXy feet higher than the sur&ee of the Baltic. 
There are^ however, in the neighbourhood of these 
formations, others precisely similar in mineral com<- 
pofiition and testaceous remains, which ascend to 
the height of between 100 and 200 feet, in which 
iao vei^e of human art has been seen. Similar de- 
posits reach an elevation of 500 and even 600 feet 
kd Norway, as in the neighbourhood of Christiania^ 
where they have usually been described as raised 
beitohes, but are, in fact, strata of day, sand, and 
koarl, often many hundred feet thick, which cover 
the inland country far and wide, filling valleys 
and deep depressions in the granite, gneiss, and 
primary fossiliferous rocks, just as the tertiary 
formations of England and France rest upon the 
chalk, or fill d^ressions in it. 

AH conchologists are agreed that the shells of 
the deposits above mentioned are nearly all, per-* 
haps all, absolutely identical with those now peo^ 
pling the contiguous ocean ; so that, in the absence 
of any evidence of their being Recent, we must 
regard them as Newer Pliocene formations* 

Along the western shores of South America, 
Recent and Newer Pliocene strata have in like 
manner been brought to li^L These often con- 
sist of enormous masses of shells, similar to those 
now swarming in the Pacific. In one bed of this 
kind, in the island of San Lorenzo, near Lima, 
Mr. Darwin found, at the altitude of eighty-five 

o 4 



296 RECBNT AND CPtetlt 

feet above the 8ea» pieces of cotton-thread, plaited 
rush, and the head of a stalk of Indian com, aB 
of which had evidently been imbedded with the 
shells. At the same height. on the. neighbouring 
mainland, he found other signs corroborating the 
cqpinion that the ancient bed of the sea had there 
also been uplifted eighty-five feet, since the region 
was first peopled by the Peruvian race. ^ But 
similar shells, or strata containing them, have been 
found much higher, almost every where between the 
Andes and sea coasts of Chili and Peru, in which 
no human remains were ever, or in all probability 
ever will be, discovered. These strata, therefore, 
may provisionally, at least, be designated Newer 
Pliocene. 

In the West Indies, also, rocks both of the Re« 
cent and Newer Pliocene periods abound. Thus, 
a solid limestone occurs at the level of the sea* 
beach in the island of Guadaloupe^ envek^ing 
human skeletons. The stone is extremely hard, 
and chiefly composed of comminuted shell and 
coral, with here and there some entire corals and 
shells, of species now living in the adjacent sea. 
With them are included arrow heads, firagments 
of pottery, and other &bricated articles. A lime* 
stone with similar contents has been formed, and 
is still forming, in St« Domingo and other islands. 

• Journal, p. 451. (for title, see note, p. 137.) 



Ch. XIV.3 NEWER PLIOCENE atTRATA. 297 

But there are also more ancient rocks inthe West 
Indian Archipelago, as in Cuba, near the Havanna, 
and in other islands in which are shells identical 
with those now living in corresponding latitudes ; 
^ome well preserved, others in casts, all referable 
to a period which, if we can depend on negative 
evidence, was anterior to the introduction of m^n 
into the New World. 

The history of Holland, during the last 2900 
yearS) makes us acquainted with a vast accession of 
Recent strata, by which parts of the sea near the 
mouths of the Rhine have been filled up and con- 
verted into dry land* But, if we ascend the Rhine, 
we ^find throughout its course, from Cologne to 
the frontiers of Switzerland, a yellow calcareous 
loaQi, called loess by the Germans, in which are 
fossil shells, both freshwater and terrestrial, of com- 
mon European species. The entire thickness of 
this loam amounts in some places to 1200 or 300 
feet, and it rises from the height of 300 to 1200 
feet above the sea. Bones of the mammoth or 
extinct elephant, together with those of the horse, 
and some other quadrupeds, have been met with 
in this Newer Pliocene formation, but no remains 
or signs of man ; and it can be proved that the 
physical geography of the whole valley of the 
Rhine has undergone enormous changes since the 
deposition of this loam. 

No marine strata of the Recent period have yet 

o 5 



ii; 



hem bM^ht lo light in Ei^iand wUch tme to 
m/ch a he^t above the letel of the sea as the 
hig^iest tides may not once have reached. Bumd 
ships have been found in the fonner channds^of 
the Bother in Sussex, of the Marsey in Koit, 
and Thames near London. Canoes and stone- 
hatchets have been dug up,.in ahnost all pasts of 
the kingdom, in peat and shdl-marl ; but there ist 
no eiridence, as in Sweden, Italy, Peru, ChiU) and 
other parts of the worlc^of thebedof the sea, and 
the ai^oiniiig ooast, having beai uplifted bo^y in 
modernr^imes, so that Recent formations have be* 
come land« There are, however, in various puts 
of Great Britain and Ireland, Newer Fliocener 
deposits of marine origin, oonsistii^ o£ sand and 
elay9 usually of small thickness ; as, for example, in 
Cornwall, and near the borders of the ' great 
estuaries of the CSyde and Forth, in Scotland, 
and in that of the Shannon, in Ireland. These 
are found usually near the coast* but in some rare 
instances they penetrate inland to a. distance of 
sixty miles ircHn the sea^ as at Bridgnorth, in 
Shropsliire.* They also rise occasionally' to great 
heights, as at Preston, in Lancashire^ where thejr 
are 350 feet above the sea; wid, what isstill more 
remarkable, on a mountain called Moel Trytanet 
in Wales, near the Menai Straits, they attain an. 

# See MurchisoQ, Proceedings of Geol. Soc^ vol. ii. p. 333. 



Ch.XIT.] KEWER BLieCBME STRATA. 299 

elevation of about 1400 feet* * la all tibese plaCM 
they^ contain sh^s indisputably of tbe 8bme*6pe^ 
imSiOA those which now people ihe Britiah^efis; 
vid althmkghy perhaps, on more aoeurate examin-* 
atioB some flight intermixture 6f ^ctinct testaeea 
will appear, yet the geologist will always refer 
them, to the most modem tertiary era. 

There are, mor«>ver, a great many freshwater 
depoidts scattered over England, which belong to 
the Newet Pliocene period, as at North Cliif, in 
the t^ounty of York, where thirteen species of 
British land and freshwater shells w^re found im- 
biedded in the same strata with the remains ot the 
bison and mammoth, f In like manner, at Crop-' 
thome, in Worcestershire, on the banks of the 
Avon, a tributary of the Severn, Mr. Strickland 
observed fluyiatile and land shells, nearly all of 
recent species, with the bones of an extinct kind 
of hippopotamus^ Recent freshwater shells also 
appear in beds of loam, together with bones of 
the deer and mammoth, in the diffs of the estuary 
of the Stour, in Suffolk. Some writers have con-' 
founded these and similar fluviatile and lacustrine 
strata, with the ancient alluviums which they 
term diluvial. 

Older Pliocene strata in England-^ Crag, — 
There are some few coimtries in Europe, as in 

* Proceedings of Geol. Soc, vol. i. p. 331., and vol. ii. p. 333. 
•f See Principles, Index, ** Mammoth." 

o 6 



3IQ0 OLDER PLIOCENE STRATA. IPviXL 

the district between the Gironde and the Pyre** 
nees, in the south of France, or that betwe^i the 
Alps, north of Vicenza, and the hills near Turin» 
in the north of Italy, where fossiliferous sti^ats 
representing all the three periods, the Eocene, 
Miocene, and Older Pliocene^ are present. But 
the tertiary deposits of England are limited to 
the Eocene and the Older and Newer Pliocene 
groups, the Mioc^ie being wanting. 

It is chiefly in the eastern part of the county 
of Suffolk that a deposit provincially named crag 
is seen in its most characteristic form. This crag 
consists chiefly of a series of thin layers of quartz- 
ose sand and comminuted shell, which rest some- 
times on chalk, sometimes on an Eocene tertiary 
formation, called the ^^ London Clay." Mr. 
Charlesworth, whose opinion I have lately had 
opportunities of confirming, has correcUy stated 
that the crag, in part of Suffolk, may be divided 
into two distinct masses, the upper of which may 
be termed the red, and the lower the coralline 

I crag.* The inferior division, however, is of very 

limited extent, ranging over an area about tw^i^^ 
miles in length, and three or four miles in breadth, 
between the rivers Aide and Stour. 

\ The red crag is generally at once distinguish- 

able from the coralline, by the deep red ferruginous 

* London and Edin. Phil. Mag. No. 38. p. 81. Aug. 1835* 



Cb.XlV.] BN6LISB CBAG. 301 

or ochreou»-colour of its sands and fossils. Its 
strata are also remarkable for the oblique or 
diagonal position of the subordinate layers (see 
p. 38.) ; and these often consist of small fiat pieces 
of shelly which lie parallel to the planes of the 
smaUer strata, showing clearly that they were so 
deposited, and that this structure has not been 
due to any subsequent rearrangement of the mass 
after deposition. That the ancient sandbanks in 
question had sometimes sides sloping in all direc- 
tions, is implied by the fact that the oblique layers 
sometimes slant towards all points of the compass 
in different parts of the same quarry. They were 
probably shifting sands, and a great proportion of 
the shells composing them have been ground down 
to small pieces, while others have been rolled ; and 
the two parts of the bivalves are almost invariably 
disunited. The red crag contains some peculiar 
fossils, and others which seem to have been washed 
out of the lower or coralline crag. Some few of 
the bivalves of the red crag are entire, with both 
valves joined. 

The coralline crag is usually free from ferru* 
ginous stains, and consists of light greenish shelly 
marl, and white calcareous sand. Sometimes it 
forms a soft building stone, in which entire shells, 
echini, and many zoophjrtes are imbedded. Here 
and there the sofler mass is divided by thin flags of 
hard limestone, in which are corals in a good state 



002 OLDER PXJOGSNE JBTEaTA. ZfuilV 

of preservatioiit which jevidnitly grew at the bottom 
of a, tnaiquil sea, in the positum in which we now 
see them. Yet the sands in this formation, as in 
the red crag, are often composed entirely of com- 
minuted shelL 

In smne places, as at Tatdngstone, in Smffi^ 
the U^logical distinction of the two drrisions, 
though perceptible, is much less marked; the in^ 
ferior crag bdng composed chiefly of greenish 
marl, with only a few stony beds. The shells also 
are mostly broken, and corab are almost as rare 
as in the red crag. 

At some places, as near Orford, the coralline 
crag is exposed at the surface, and the bottom of 
it lias not been reached at the depth of fifty feet. 
Yet not fiff fi-om this town, the sur&ce is occupied 
exclusively with red crag, which rests immediately 
upon the London clay. Wherever the two divi- 
sions are found together, the coralline mass is the 
lower of the two, and is interposed between the 
red crag nnd London clay ; and the strata of the 
upper and lower crag are unconformable one to 
the other, as in the section represented in the 
annexed diagram, which I have myself examined. 

Fig. 128. 

Sbottisham , 

Itaiton. Creek. RannlMlt. 1 



Section near Ipswich^ in St^olk, 
a. red crag. b. coralline crag. c London clay. 



i:h.xivj EHauaa cbao. go3 

• In flie places here referred to, the coralline crag 
varies in fliickness firom fifteen to more than 
twenty feet, and th^ red crag is often much 
thicker. 

Amongst upwards of 400 species of testaoea 
found in the crag, there are many common to 
both diviaioHB ; but some, which are very abundant 
in the red, have never been met with in the coral- 
fine crag ; as, for example, the Fusas contrariui 
(Fig. 1291), and several species of Nassa and 

FouOs ekaracterutk of lie Red Crag. 
Fin. 139. 




i 



Nun, 
Fig, 132. 



Murex(BeeFigs. 130, 131.), which two genera seem 
never' to have been discovered in the lower crag. 
On the other hand, scarcely any corals have been 
found in the red crag. These abound in the in- 
fepior diKsttn, and some of them are of a globular 
form, and belong to the genera Theonoa (Lamo- 
roux), Cellepora, and a third to Fascicularia, which 



304 OLDZK PLIOCWra STBATA. [Fm 11 

is of Tery pecaliw structiire, nnknown in the liv- 
ing creation. (See Fig. 138.) 

Kg. 183. 




oj (/an hMv« gcmit,^am Ue b^triar 

or eoraUii etat, Si^ffiilli. 

a. eilerior. b. Tcitkal Mction of interior. 

c. portion of exterior iiiBgiii6ed. 

d. portion of interior magnified, showing that it ii made up of 
long, thin, itrught tubes, united in conical bundles. 

The general analogy of the crag aheUe to those 
now living in the neighbouring seas, between the 
latitudes 50° and 60° north, b so striking that we 
cannot hesitate to refer the formation to the Plio- 
cene period; but, as all conchologists are agreed that 
more than half the species are extinct or unlcnown, 
it b to the Older and not the Newer Pliocene 
period that they belong. Dr. Beck, after examin- 
ing 260 species of these shells, in&nnB me that 
the average number of species to geoer* is such 
as iadicates a temperate climaK, a result which is 
also confirmed by the large development of cer- 



olxiv.] skoluh crag. 300 

tain northern forms, such as the genuB Aatsrte 
(see Fig. 134.), of which there are about iburteen 
species, many of them being rich in individuals; 
and there is an absence of genera peculiar to hot 
climates, such as Conus, Oliva, Mitra, Fasciotaria, 




Jitarlt, (Cnunw, Idm.) j qwoVt 



and others. The cowries (Qfpraia) (Fig. 132.) 
also ^% small, as in the colder regions. A large 
volute, called Foluta Lamberti (Fig. 135.), may 
Fig. 1S5. seem an exception ; but it differs in 
form from the volutes of the torrid 
zone, and may, like the large Vobtta 
MoffeBanica, have been extra-tropicaL 
When I first submitted the shells of 
^ the crag to M. Deshayea, in 1629, he 
recognized their general resemblance 
to the fauna of the German ocean, and 
^j;^„,j,^ determined that out of 111 species 
»™« '"*''"■ there were 45 identical with those 
now living. Dr. Beck, on the other hand, who 
has since seen much larger collections, considers 
that almost all the epeciea are distinguishable from 



^0Q OLDER PLIOCENE STRATA. C^aktll. 

those now living, aad this subject is still under 
discussion. 

It has been asked whether, as the upper and 
lower crag of .Suffolk differs greatly in mineral 
composition and fossils, they may not belong to 
two different tertiary periods. To this I may 
reply, that the general character of the shells is 
the same, and by no means leads to such a conclu- 
sion. The two deposits may have been going on 
contemporaneously under different geographical 
conditions in the same sea. One region of deep 
and clear water, far fi*om the shore, may have 
been fitted for the growth of certain corals, echini, 
and testacea ; while another shallower part nearer 
the shore, and more frequently turbid, or where 
sand and shingle were occasionally drifted along, 
may have been favourable to other species. After 
this, the region of deep and tranquil water becom- 
ing shallow, or exposed to the action of waves and 
currents, a formation like the coralline crag may 
have been covered over with sandy deposits, such 
as the red crag, and many fossils of the older 
beds may have been washed into the newer strata. 
If a considerable lapse of time intervened in a 
particular spot between the conversion of a deep 
sea into a shoal, some small change in organic life 
may have taken place, and consequently the dis-< 
tinctness in character of the fossils of the two 
formations may be derived from two causes, first 



Ch. XIVJ ISNOLUH CRAC^. ^07 

sCnd principally tke difference of geographical coh- 
ditions, and, secondly, that law of the coming in 
aiid going out of species which was alluded to in 
the last chapter, (p. 275.) 

The area over which both divisions of the 
6rag can be traced is too small to enable us to 
arrive at satisfactory conclusions on a question of 
such magnitude; but the section given above 
(p. 302.) shows distinctly that, near Sutton, the 
Iowa* crag had suffered much denudation before 
the deposition of the red crag. At D (Fig. 128.) 
there is not only a distinct cliff, eight or ten feet 
high, of coralline crag, running in a direction 
N. E. and S« W., against which the red crag abuts 
with its horizontal layers, but this cliff occasionally 
overhangs. The rock composing it is drilled 
everywhere by Fholades belonging to the period 
of the red crag. The cliff may have been caused 
by submarine denudation, in a shallow sea; and 
had the red crag been equally solid, it would 
probably have presented many similar perpendi- 
cular difls ; for beds, ten or twelve feet thick, of 
loam or sand, in this formation^ are often seen to 
be unconformable to older beds, which have been 
in part cut away. Similar excavations are now 
made, even on a larger scale, by the sea, in the 
great sandbanks off Yarmouth, in part of which 
Captain Hewett, R. N., found, in 1836, a broad 
channel, sixty-five feet deep, where there had been 



308 EOCENE STRATA. C^tft IL 

only a depth of four feet in 1822. This r^nark- 
able change was ascertained during two hydro- 
gnqphical surveys, in the years above mentioned, 
and shows how denudation, amounting to sixty 
feet in vertical depth, can take place under water 
in the course of fourteen years. The new channel 
thus formed, serves now (1838) for the entrance 
of ships into Yarmouth Roads. 

Eocene JbrmaH&ns in Enghmd — London day. — 
In the section already given of the tertiary strata 
of Suffolk (p. 302.), it will be seen that the crag 
rests on a formation called the London clay, which 
there consists of alternating beds of blue and brown 
day, with many nodules of calcareous stone, used 
for Roman cement. This formation is well seen 
in the neighbouring cliffs of Harwich, where the 
nodules contain many marine shells, and some- 
times the bones of turtles. The relative position 

Fig. 1S6. 
Crag, London cUy. Chalk. 

} f ^ — r 



of the chalk, London clay, and crag, between the 
coast of Essex and the interior, may be under- 
stood by reference to the annexed diagram. The 
London clay has been so named, because it oc- 
curs in the neighbourhood of the metropolis, in 
a trough or basin of the chalk. (See section, 
p. 816.) We know, by numerous borings made for 



ph.2uyg jjondon clay. S09 

water, that the chalk exists everywhere below, after 
we have penetrated through clay and sand to the 
depth of from 200 to 600 feet; and, if we proceed 
to the south of London, we find the chalk rising 
up to the surface and forming the Surrey hills ; 
while if we proceed northwards, into Hertford- 
shire, or, westward, by the Thames, into Oxford* 
shire, we again meet with the same chalk. 

The overlying Eocene deposit consists of two 
portions ; the upper of blue clay, with occasional 
cement stones, as before mentioned ; the lower of 
various coloured sands and clays; the fossils 
throughout all the beds being very different from 
those of the crag. Scarcely any one of the sheHs 
can be identified with species now living; and 
the whole assemblage is such as to resemble the 
testaceous fauna of the tropics. This opinion 
is favoured by the occurrence of many species 
of Mitra and Voluta, a large Cypraea, a very large 
Rostellaria, and shells of the genera Terebellum, 
Cancellaria, Crassatella, and others, with four or 
more species of Nautilus. (See Figures, p. 310.) 
There are fish, also, which indicate a warm climate ; 
among which may be mentioned a sword-fish, ( Tet^ 
rcptenupriscuSf Agassiz,) about eight feet long, and 
a saw-fish, (Pristis bisulcatus, Ag.) about ten feet 
in length ; genera foreign to the British seas. 

These last have been found in the island, of 
Sheppey, which is composed of London clay, where 



S12 FOSSIL MAMMALIA. tP»*t It 

near Auch, in the department of Gers, about forty 
miles west of Toulouse, where the bones of an ape^ 
or gibbon, accompanied those of the rhinoceros, 
dinotherium, mastodon^ and others ; in India, by 
Captain Cautley and Dr. Falconer, who found the 
remains of a monkey, with the bon,es of many ex- 
tinct quadrupeds, in . the Sewalik hills, a lower 
range of the Himalaya mountains, near Saharun-. 
pore. 

The frequent occurrence in the tertiary strata 
of fossils referable to the highest class of verte- 
brata is a &c!t the more worthy of notice, as we 
shall find in the sequel how great is their rarity 
in the secondary formations. 



313 



CHAPTER XV. 

CRETACEOUS GROUP. 

White chalk — Its marine origin shown by fossil shells — 
Extinct genera of cephalopoda — Sponges and corals in 
the chalk — No terrestrial or fluviatile shells, no land 
plants — Supposed origin of white chalk from decomposed 
corals — Single pebbles, whence derived — Cretaceou^ 
coral-reef in Denmark — Maestricht beds and fossils — 
Origin of flint in chalk — Wide area covered by chalk — 
Green-sand formation and fossils — Origin of — External 
configuration of chalk — Outstanding columns or needles 
— Period of emergence from the sea — Difference of the 
chalk o£ the north and south of Europe — Hippurites — 
Nummulites — Altered lithological character of cretaceous 
formation in Spain and Greece — Terminology. 

The next group which succeeds to the tertiary 
strata m the descending order has been called 
Cretaceous or chalky, because it consists in part 
of that remarkable white earthy limestone called 
chalk {creta). With this limestone however are 
usually associated other deposits of sand, marl; 
and clay, called the Green-sand formation, be- 
cause some of its sands are remarkable for their 
bright green colour* 

The following are the subdivisions into which 
the Cretaceous Strata have been divided in the 
south of Cngland : — 



314 



CRETAqS0U3 OROUP. 



C Put II. 



Cretaceous 
group. 



1. Chalk 
formation. 



2. Green-sand 
formation. 



'a, softwhite chalk, with "^ united 
flints - - .1 thickness 

b. hard white chalk,with >from 600 
few or no flints - | to 1000 

c. chalk marl - .J feet.* 

r thickness 

a. upper green-sand -< 30 to 100 

(^feet. 

b. Gaultf or blue marl, 10 to 150 ft. 

c. lower green-sand and 1 
iron-sand, with occa- L 250.f 
sional limestone -J 



The accompanying section (Fig. 143.) will show 
the manner in which the tertiary strata of the 
London and Paris basins, as they are called, rest 
upon the chalk, and how the white chalk in its 
turn reposes throughout this region upon the 
green-sand formation. 

I shall now speak first of the chalk, its fossils, 
and probable origin ; and then say something of 
the green-sand ; after-which I shall point out the 
probable relations of the chalk and green-sand to 
each other. 

White Chalk. — The white chalk used in writing 
consists almost purely of carbonate of lime. Al- 
though usually soft, this substance passes in some 
districts by a gradual change into a solid stone 
used for building. The stratification is often ob- 
scurie, except where rendered distinct by alternat- 
ing layers of flint. These layers are from two to 
four feet distant from each other, and from three 

* Conybeare, Outlines, &c., p. 85. 

f Fitton, Geol. Trans., Second Series, yol>iy. p.B19. 



.«i.xyo 



fOSBllA X>F.THE CHALK. 



m& 











I 



t 

» 



I 

2 



I 



^sfe^ 



iv^l 




.c 



I 

I 



I 



to six inches in thickness, oc- 
casionally in continuous beds, but 
more frequently in nodules. 

The annexed figures represent 
some few of the fossil shells which 
are abundant in the white chalk, 
and these alone are sufficient to 
prove its marine origin. Some 
of them, such as the Terebratulae, 
(see Figs. 148. 150, 151, 152.) 
are known to live at the bottom of 
the sea, where the water is tran- 
quil, and of some depth. The 
Crania and Catillus (Figs. 145. & 
144.) may be pointed out as forms 
which, so far as our present in- 
formation extends, became ex- 
tinct at the close of the cretaceous 
period, and are therefore never 
met with in any tertiary stratum, 
or in a living state. Among other 
forms, equally conspicuous among 
the fossil moUusca of the creta- 
ceous group, and foreign to the 
tertiary and recent periods, may 
be mentioned the Belemnite, Am- 
monite, Baculite, and Turrilite 
of the family Cephalopoda, to 
which the living ^uttle-'fiah and 
nautilus belong. 
p 2 



roflsiLs or tbe.chaue 



FOSSILS OF THE WHITE CHALK. 
Fig. I'M. 





li>U|>|« 



FOSSIL CEPHALOPODA OF EXTINCT OENEBA. 

Crtlacanu Period. 

« £lg. 154. b 




White Chalk ud Vrpa GwttB'it 



One of these, the Belemnite, like the bone of 
the common cuttle-fish, vas an internal shell. Be- 
p 3 



yosfiLS or TIB CBalk. 



(FutlL 



sides these there are other fitsdls in the chalk, 
such as sea-urchins, corals, and sponges (see 
Figures), which are alike marine. They are dis- 
persed indifierently through the soft chalk and 
the hard flint. 

Fig. 15B. 





To some of these inclosed zoophytes many flints 
owe their irregular forms, as in the flint repre- 
sented in Fig. 161., where the hollows on the ex- 
terior are caused by the branches of a sponge, 
which is seen aa breaking open the flint. (See 
Fig. 160.) 



Ch.XV.]' OBlQliU OF WHITK CHALK. 

Fig. 100. Fig 181 




JbrmnMiigipmigehtBjaitl/ramardiali.* 

With these fossils the remains of fish and Crus- 
tacea are not uncommon ; but we meet with no. 
hones of land animals, nor any terrestrial or fluvi»- 
tile shells, nor any plants, except pieces of drifl; 
wood and sea-weed, nor any sand or pebbles ; all 
the appearances concur in leading us to believe 
that this deposit was formed in a deep sea, far from 
land, and at a time when the European &una was 
pwfegtly distinct from that of the tertiary period,' 
&om which its numerous speCies of plants and 
Viimak entirely differ. 

Origin of the White Chalh. — Having then come 
to the conclusion, that the chalk was formed in an 
open sea of some depth ; we may next inquire, in 
what manner so large a quantity of this peculiar 
white substance could have accumiUated over an 
area many hundred miles in diameter, and some 
of the extreme points of which are distant, as we 
shall see in the sequel, more than 1000 geogra- 
phical miles from each other. 

« From the coUeccioii of Mr. Bowerbanfc- 
P 4 



WIX ..13 



It wM ^itialfted in an early poit of tih& Yolmn^^ 
that some even of that chalk wfaicn appears to an'. 
ordiriaFj observer quite destitute of organic re- 
mains, is nevertheless seen under the micrbscope 
to be fell of fragments of corals and sponges ; the 
valves of Cytherina, the shells of fbraminifera, and 
still more minute infusoria. (See p. 55.) 

Now it had been often suspected before these 
discoveries, that white chalk might be of animal 
origin, even where every trace of organic structure 
has vanished. This bold idea was partly foimded 
on the fact, that the chalk consisted of pure car- 
bonate of lime, such as would result froih the 
decomposition of testacea, echini, and corals, and 
in the passage observable between these fossils 
when half decomposed into chalk. But this con- 
jecture seemed to many naturalists quite vague 
and visionary, until its probability was strength- 
ened by new evidence brought to light by modem 
geologists. 

We learn from Lieutenant Nelson, that, in the 
Bermuda islands, there are several basins or la- 
goons almost surrounded and inclosed by reefi <^ 
coral. At the bottom of these lagoons a soft 
white calcareous mud is formed by the decompo- 
sition of Eschara, Flustra, Cellepora, and other 
soft corallines. This mud, when dried, is undis- 
tinguishable from common white earthy chalk*; 
and some portions of it, presented to the Museiua 



of the Gee^logpcaL Sode^ of LoBdQEBf^ migb^> after 
fuU e9E99unatiojii» be mistakmi for aneieol; cba&» 
but for tjbe labels attached to theisu About dur. 
same time Mr. C« Darwin observed siaiilar fiictsh 
in the coral islands of the Pacific; and came also 
tq tbe opinion^ that much of the soft white miuL 
found at tbe bottom of the sea near coral reefs 
has piissed through the bodies of worms, by which 
the stony masses of coral are everywhere bored; 
and other portions through the intestines of fish; 
fyr certain gregarious fish of the genus Sparua are 
visible through the dear water, browsing quietly, 
in great numbers, on living corals, like grazing 
herds of graminivorous quadrupeds. On opaaing 
their bodies, Mr. Darwin found their intestines 
filled with impure chalk. This circumstance is. 
the more in point, when we recollect how the fos- 
siUst was formerly puzzled by meeting witb cer- 
Fig. 162. Fig. 163, tain bodlcs, called cones of th^ 

larch, in chalk, which were 
afterwards, recognized by Dr. 
Buckland to be the excre* 
ment of fish.* These spiral 
coprolites (see Figures) like 
^'SS^il^^lfcSwar the scales and bones of fossil 
fish in the chalk, are composed chiefly of phosphate 
of lime. 

** Gteol. TranB.« Second Series, yoUiii. p. 833. plate 81. 
figB^aandll. 

P 5 




322 TtMBlXA IN CHALK* c^ftn. 

Shiffk pebbles in chaJk* — The general absence of 
sand and pebbles in the white chalk has been already 
mentioned ; but the occurrence here and there of 
a few isolated pebbles of quartz and green-schist, 
some of them two or three inches in diameter, in 
the south-east of flngland, has justly excited much 
wonder. If these had been carried to the spots 
where we now find them by waves or currents 
from the lands once bordering the cretaceous sea, 
how happened it that no sand or mud were trans- 
ported thither at the same time? We cannot 
conceive such rounded stones to have been drifted 
like erratic blocks by ice *, for that would imply 
a cold climate in the cretaceous period; a sup- 
position inconsistent with the luxuriant growth of 
large chambered univalves, numerous corals, and 
msmy fish, and other fossils of tropical forms. 

Now in Keeling Island, one of those detached 
meusses of coral which rise up in the wide Pacific, 
Captain Ross found a single fragment of green- 
stone, where every other particle of matter was 
calcareous; and Mr. Darwin concludes that it 
must have come there entangled in the roots of a 
large tree. He reminds us diat Chamisso, a dis- 
tinguished naturalist who accompanied Kotzebue, 
d^ms, that the inhabkants of the Radack archi- 
pelago, a group of lagoon islands, in the midst of 

« See p. 136. 



CSi. XV.] WHENCE DERIVED. ^£{9 

the Pacific, obtained stone$ for sharpening their 
instruments by searching the roots of trees which 
are cast up on the beach.* 

It may perhaps be objected, that a similar mode 
of transport cannot have happened in the creta- 
ceous sea, because fossil wood is very rare in the 
chalk. Nevertheless wood is sometimes met with, 
and in the same parts of the chalk where the 
pebbles are found, both in soft stone and in a 
silicified state in flints. In these cases it has often 
every appearance of having been floated from a 
distance, being usually perforated by boring-shells, 
such as the Teredo and Fistulana. J 

The only other mode of transport which sug- 
gests itself is sea-weed. Dr. Beck informs me, 
that in the Lym-Fiord, in Jutland, the Fucus vest" 
ctdosus^ sometimes grows to the height of ten feet, 
and the branches rising from a single root, form a 
cluster several feet in diameter. When the blad- 
ders are distended, the plant becomes so buoyant 
as to float up loose stones several inches in dia- 
meter, and these are often thrown by the waves 
high up on the beach. The Pueus giganteus^ of 
Solander, so common in Terra del Fuego, is said 
by Captain Cook to obtain the length of 360 feet, 
although the stem is not much thicker than a 

♦ Darwin, p. 549. Kotzebue's First Voyage, vol. iii. 
p. 155. 

f Mantell, Geol. of S. £. of England, p. 96. 

p 6 



lM»'8 'iJ^WiiU It ]» ^en Biet wilb flofttiipgijiJi 
i^«^ with shells attadied, sevf^al biiitdi«d.]ii3fl9 
from tbe epato wbere k grew* Some of .ibeift 
pilaiits, says Mr. Darwin, were fomid acjheriiigtl^ 
large loose stones in tbe inland channels <if .Tneri 
del Fu^o» daring tbe voyage of the Bea^ hx 
1834; and that so firmly, that the stones nere 
drawn up from the bottom into tbe boat, althoi^giit 
9P heavy that they could scarodty be lUted in bgr. 
one person.* Some foa&il sea^weeds have been 
found in the cretaceous formation, but none^ aa 
yet, of large size. 

Cretaceous coral reef in Denmark. — Having said 
so much on the probable derivation of chalk from 
the decay of corals and shells,' I may add, that in 
the island of Seeland, in Denmark, there is a yel- 
low limestone intimately connected with the chalky 
^d containing a vast number of the same fi)ssils, 
which consists of an aggregate of corals, retaining 
their forms a3 distinctly .as the dead zoophytes 
which enter into the structure of reefs now grow-* 
ing in the sea. The thidkness of this rockis un-« 
known, but it has been quarried at Faxoe to the 
depth of forty feet. At Stevensklint, in Seeland^ 
it is seen to rest on white chalk with flints, from 
which it differs greatly in appearance, and whero 
it is covered again by another limestone, whidi 

♦ Darwin, p. 303. (For full reference see p. 137.) 



Maw^ of hter diite^ agrees noi^ nearty wMl 
fhe^irUte chalk, both in fossils and auneraif cboK 
tMter. Odt of 104 species of qxfngesy corals, and 
df^r soophjtes, collected from the limestone of 
Fkooe, and from the ordinary wUte cfaaOc of Det»- 
mark, wluch agrees with that of England, no less 
dian forty-two are common to both formations; 
and many of the same species of bivalve shells 
and echinodermata have been found in both* 
The Faxoe formation, however,* is not only re- 
markable for the number and good preservation 
of its fossil corals, but also from the generic re- 
semUance of many of its univalve sheUs to fonns 
usually supposed to appertain chiefly or exdu-^ 
sively to the tertiary period. Thus among the 
pateUilbrm univalves, we find Piatdla and Enuuv 
giDula, and among the q>iral, the £dUowing g^iera, 
Cj^rsea, Oliva, Mitra, Cerithium, Fusus, Trochus, 
Triton, Nassa, and Bulla. 

The species however do not agree with those 
of the tertiary strata, and are associated with 
cephalopoda of those extinct fiunilies before men- 
tioned as characteristic of the cretaceous, and 
fiMreign to the tertiary epoch; as, for example, the 
ammonite, belemnite, and baculite. Two species^ 
the Bdemnites mucronatus (Fig. 155.), and the 
BaeuHtes Fangasii (F^. 156.), being common to 
the Faxoe beds and the white chalk. 

From these facts, we may conclude that the 



9S^ CKETACS0IJ9 OWlUP. (Fhft 11/ 

Fazoe limestone was fiyrmed in the cretaceous 
sea, in a spot fayourable fer tke multiplication of 
stony eonds and uniTalve shells^; and as some 
^ttisil portions of the rock consist of white earthy 
chalk, this latter substance must have been pro- 
duced simultaneouidy, and some of it may have 
Been washed away, in the form of mud, from the 
coral reef of Faxoe, and dispersed over the deeper 
parts of the same ocean, jnst as the white mud, 
swept out of the lagoons of the Bermudas or coral 
islets of the Pacific, must form deposits of white 
chalk, covering much wider spaces than those oc- 
cupied by the reefs. 

The same remarks apply to a rock, which re- 
poses on the Upper Chalk with flints, at St. Peter's 
Mount, Maestricht, and at Ciply, near Mons. It 
is a soft yellowish stone, not very unlike chalk, 
and ^ includes siliceous masses, which are much 
more rare than those of the chalk, of greater bulk, 
and not composed of black flint, but of chert and 
calcedony.*' * Like the Faxoe stone, it is cha- 
racterized by a peculiar assemblage of organic re- 
mains which are specifically distinct from those of 
the tertiary period, but many of them common to 
the white chalk. 

As these Maestricht beds have been thought to 
be intermediate in character between the second- 

* Fitton, OeoL Proceedings, 1830. 




ary and tertiary ifbnnatioiia, it may be proper to 
mention, as opposed to this opinion, that the Am- 
monite (Fig. 164.), Bacnlite, Hamit^ and Hip- 
puiite, have been found in 
the Maestricbt limestone 
genera which have not yet 
been detecKd in strata 
newer than the chalk. la 
the same formation, also, 
jmniam^i BMnMutnau. large turtieshave been foiuid, 
HuDiur. auj a gigantic reptile, the 

Mosasaurus, or fossil Monitor, some of the ver- 
tebra: of which appear also in the English chalk. * 
The osteol(^cal characters of this oviparous qua- 
druped prove it to have been intermediate be- 
tween the living Monitors and Iguanas ; and, frmn 
the size of the head, vertebrs, and other bones, 
it is supposed to have been twenty-four feet in 
length. 

The existence of such turdes and saurians 
seems to imply some Qeighbouring land, on the 
sandy shores of which these creatures may have 
laid their eggs. But a few small islets in mid 
ocean, like Ascension, so much frequented by 
turtles, may perhaps have afforded the required 
retreat to these cretaceous reptiles. 

Oriffin of the Jiint in chalk. — It is difficult to 

* See Mantell's Geol. of S. E. of En^and. 



928 CBAUL TLom. tPMtu- 

me a satb&ctQiy c^lanation of the origip of ^b^ 
flint in chalk, whether it occurs in noduleai oi; 
cbntinaous layers. It seems that there was ori-* 

* • • * 

ginally siliceous as well as calcareous earth in the 
muddy bottom of the cretaceous sea, at least when 
the upper chalk was deposited. Whether both 
these earths could have been alike supplied hj 
the decay of organic bodies may be matter of 
speculation ; but what was ssdd of the origin of! 
Tripoli (see p. 51.) shows how microscopic infu- 
soria can give rise to dense masses of piu^ flint. 
The skeletons of many living sponges consist of 
needles or spicula of flint, and these are found 
very abundantly in the flints of the chalk. There 
are also other living zoophytes, which have the 
power of secreting siliceous matters from the 
waters of the sea, just as mollusca secrete cal- 
careous particles. 

From whatever source the mud derived its 
silex, we may attribute the parallel disposition of 
the flinty layers to successive deposition. The 
distances. between the layers, says Dr. Buckland, 
must have been regulated by the intervals of pre- 
cipitation, each new mass forming at the bottom 
of the ocean a bed of pulpy fluid, which did not 
penetrate the preceding bed on which it rested, 
because the consolidation of this last was so far . 
advanced as to prevent such intermixture.* Never- 

* Oeol, Trans., First Series, vol. iv. p, 420. 



OLXV.J^ AREA COVERED BT CHALK. S^d 

theless the separation of the fimt into layers, so^ 
dbtinct from the chalk, Is a singular phenomenon, 
and not yet accounted for. Perhaps, as the specific 
gravity of the siliceous exceeds that of the cal- 
careous particles, the heavier flint may have sunk 
to Uxe bottom of each stratum of soft mud? 
^ Geographical extent of White Chalk* — The area 
aver which the white chalk preserves a nearly 
homogeneous aspect is so great that geologists 
have often despaired of finding any analogous de* 
posits of recent date ; for chalk is met with in a 
north-west and south-east direction, from the north 
of Ireland to the Crimea, a distance of about 
1140 geographical miles, and in an opposite di- 
rection it extends from the south of Sweden to 
tiie south of Bordeaux, a distance of about 840 
geographical miles. But we must not conclude 
that it was ever spread out uniformly over the 
whole of this vast space^ but merely that there 
were patches of it, of various sizes, throughout 
this area. Now, if we turn to those regions of the 
Pacific over which coral reefs are scattered, we 
find some archipelagoes of lagoon islands, such as 
that of the Dangerous archipelago for instance, 
and that of Radack, with some adjoining groups, 
which are from 1100 to 1200 miles in length, and 
300 or 400 miles broad ; and the space to which 
Flinders proposed to give the name of the Coral- 
lian sea is still larger ; for it is bounded on the. 



SSX^ GBEEV-aAliD FOBMATIOK. tftMVL 

east bj the Australian bamer, on the west by 
New Caledonia, and on the north by the reefii 
of Louisiade. Although the islands in tliese 
spaces may be thinly sown, the mud of the decom- 
posing zoophytes may be scattered far and wide 
by oceanic currents. 

Oreen^sand formation. — The lower division of 
the Cretaceous group in England is divisible, as 
wie have already seen, into Upper Green-sand, 
Gault, and Lower Green-sand. The green*grains 
have been found, by analysis, to consist chiefly oC 
silicate of iron, and they agree in composition 
with chlorite. The inferior white marly chalk 
becomes more and more charged with these grains 
imtil it passes into the upper green-sand, a fonn- 
ation of sand and sandy inarl, frequently mixed 
with chert, and this again passes downwards into 
the day aiid marl, pf ovincially called Gault. Both 
of these subdivisions, altfiough often diminishing 
in volume to a thickness of two or three yards, 
form distinct and continuous bands of sand and 
clay between th6 chalk and lower green-sand 
throughout considerable tracts in England, France, 
and Belgium ; and each preserve throughout this 
space certain mineral peculiarities and character- 
istic fossils. 

Ilhe lower green->sand below the gault is formed 
partly of gre^en and partly of ferruginous sand 
and sandstone, with somie limiestone. These rocks* 



Gb, XV'T ORKKtJAIlO FORMATION. 38£ 

sDeoded each other in the foUowing descending 
order in Kent ; — 

foruginoui, wilh concretioiu 
- 70 feet. 

3. Saod with green nutter - - TO lo 100 feet. 

3. Calcareaos stone, called Kentish rag . 60 to 80 feet." 

The iossils of the green-sand are marine, and 
some of them, like the Pecten tpiinguecostatus 
{Fig. 166.), range through all the members of the 

FOSSILS OP THE GREEN-SAND FORMATION. 






a. Ter^alala lnTa. 7 Uppergreen-uni PecUnSiialaHa. 

b. Smite, leet in rr^/Ue.i France. Upper uid lowtr 

Fg 167 




series. Several forms of cephalopoda, such as the 
Hamite (Fig. 167.), Scaphite, and others diatin- 



• Rtton, Geol, Trans., Second Series, vol.r 
flbiA-pl. IS. 



guiab'the ^Gjfeen^wiid fiunnatioii i&.£ii^ttid- fiaom 
the White Chalk. 

./• Oriffin of the Greenr^andJmnati(mm''^\Jvliket^ 
white chalk, this deposit consists of a suecessicm 
of ordinaiy beds of sand, clay, marl, and impme 
limestone, the materials of which might result 
from the wearing down of pre-existing rocks. 
The nature of these derivative rocks we learn, 
from finding in the green*sand pebbles of quartz, 
quartzose sandstone, jasper, and flinty slate^ toge- 
ther with grains of clilorite and mica.* Butwe natu- 
rally inquire, how it could happen that, throughout 
a large submarine area, there should be formed, 
first, a set of mechanical strata, such as the 
green-sand, and then over the same space a pure 
zoophytic and shelly limestone, such as die white 
chalk. Certain causes, which during die first 
period gave rise to deposits of mud, sand, and 
pebbles, must subsequendy have ceased to act ; 
for it is evident diat no similar sediment disturbed 
the clear waters of the sea in which the white 
chalk accumulated. The only hypothesis which 
seems capable of explaining such changes is die 
gradual submergence of land which had been 
previously exposed to aqueous denudation. This 
operation may have gone on with such slowness 
88 to allow time for considerable fluctuations in die 

* Htton, Geol. Trans., Second Series, voLiv. p. 116, 



ei.4&V.;) OREBIMASD «Da]ll4TION. 

stnlxi of the oiganic ivorld^ so that ditteteat scHs a( 
strata, beginning with the lower greenHEnnd, uid 
ending with- the upper white chalk, may each ebn* 
tain some peculiar remains of animals which lived 
suocessiTely in the sea; while some c^)eGie8 niay hate 
continued to exist throughout the whole period^ 
fflidare iherefinre eominon to all these formations. 
.It will be seen in the next chapter, when we 
treat of the strata called the Wealden, that such a 
general subsidence of land as is here supposed to 
explain the manner in which the chalk succeeds 
the green^sand, maj be inferred fixHn other inde« 
pendent proo& to hare taken place throughout 
large areas. 

It cannot however be assumed, that all the 
green-sand in Europe had ceased to be deposited 
before any chalk began to accumulate. Such 
indeed was the order of events in parts of Eng<* 
land, France, Belgium, and D^unark ; but if we 
compare different countries, and some of these 
not far distant from each other, we find reason to 
believe that sand and clay continued to be thrown 
down in one plaoe^ while pure chalk was forming 
in another. In Westphalia, for example, strata 
containing the same fossils as the white chalk of 
England, consist of sand and marl wilii green 
frrcdns like the upper gre^>«sand. Similar foots 
have been observed in Hungary in the Carpatluan 
mountaui chain. Such variations would occur if 



934 EXTERNAL COHFISDRATfOlf OF CHALK. IPtfttlt 

the supposed sinking down of land did not take 
place simultaneously everywhere; and for this 
leeson the minor subdivisions of the cretneeous 
group, however persistent and uniform in their 
mineral characters in some regions, vary rapidlji) 
and change entirely in other directions. 

External amfiffuratian of Chalk. — The smdoth 
rounded outline of the hills composed of white 
chalk is well known to all who have travelled in 
the south-east of England. The chalk downs, 
being free from trees or hedge-rows, affi>rd us an 
opportunity of observing the manner in which the 
upper valleys unite with larger ones, and how these 
become wider and deeper as they descend. For 
the most part they are dry, yet occasionally they 
a£Pord a perfect system of drainage, when a sudden 
flood is caused by heavy rains or the melting of 
snow. We may conceive their excavation to hav^ 
been caused by the action of the waves and cur- 
rents while the chalk was gradually emerging 
from the sea. To the same action we nuty ascribe 
the escarpments as they are called, or those long 
lines of precipitous clifi^ in which the chalk ofiteti 
.terminates abruptly, and which, though now in- 
land, have been undermined by the waves when 
the chalk was upheaved from the sea. 

Many examples occur in England; but there 
are no precipices of chalk more striking t^ a rt 
those which bound the lower part of the great 



valley or goi^ through which the S«ne flows in 
Normandy. At various heigfau on the steep sides 
of these hilla are outstanding pillars and pinnacles 
of a very hard and compact chalk, as at Toume- 
dos and Elbeuf, near Bouen, which evidently owe 
their shape to the power <^ the waves. (See Figures.) 




Some small columns near Elbeuf exhibit parallel 
and horizontal grooves scooped out of the columns 
at different heights. (See Fig, 170.) These greatly 
resemble certain limestone pillars, described by 
Ct^tain Bayfield, in the Mingan islands in the 
gulf of St. I.awrence. There is evidence there 
of the coast having been upheaved at successive 
periods, so that p^allel ranges of sea beaches, 
with recent shells, loiv^ heMi laid dry, terrace above 



$0 ^mM-^imtHmr «*»« 

Uite iaolatcd.jpBMa of. o«loftre*uk rode maf^ dib 

indioitf* pauwe in.'^ uphuvii^ praoesi^ -Atrii^' 
i^hkh t^ KB. had a OoDudmafcile Aie to'-'WMr 
AWf^ die stone B8 Tell as to-lhnMr-U{l tfbauduM 
tlie sameleveL* '■"■ 

The oacdles of the Isle of Wight, and tbe Ord- 
Harry Bocks of the coast of Dorsetshire, are' well' 
known to those who h&Te examined the dia& 
cliffe of the South of EUigland. Besides Ae mkud 
cQlumns in Normandy, above described, there are 
others more recently formed on the Bea coast of 
that same country. 

Fig. 171. 




If we inquire at what period tlie e 
and denudation of the cretaceous rocks took plac^ 

* Captmn Bayfidd, Oeol. Trans., Second Series, toI. v. 
p. H. Abo Princ. of OcdL, lodes, " Nupbca lEUnid." 
t Setn^Inferieore, p. 1^ and plate 6. fig:. 1, 



wmMlk^tiA itmtit oo&afreA in great part after 
iibt» fkpMtkm of TRrious marine tertiiiy feim- 
■rfitwn^ «p dial both the cretac^uB and tertiary 
iKBds . "^ifefe iqpmsed together. The greatest eleva-^ 
tion which the chalk reaches in England, is the 
auminit of Inkpen- Beacon in Berkshire, which id 
1011 feet above the sea; but marine deposits 
of the flame age attain an elevation of 8000 feet in 
the Alps and Pyrenees. These may have partly 
^neiged during the cretaceous period, just as the 
coral ree& in some regions of the Pacific are 
growing in one spot, while other portions of the 
same have been uplifted by subterranean forces, 
and converted into land. 

Difference between the chalk of the north and south 
of Europe. — By the aid of the three tests of relative 
age, namely, superposition, mineral character, and 
fossils, the geologist has been enabled to refer to 
the same cretaceous period certain rocks in the 
north and south of Europe, which differ greatly 
both in their fossil contents, and in their mineral 
composition and structure. 

If we attempt to trace the cretaceous deposits 
fix)m England and France to the countries border- 
ing the Mediterranean, we perceive^ in the first 
place, that the chalk and green-sand in the neigh- 
bourhood of London and Paris, form one great 
continuous mass, the strait of Dover beiug a trifling 
interruption, a mere valley with 'chalk cliffs on 

Q 



ass 



DIFFEREMT CHARACTEK OP CHALK t^Mt IL 



both side& We tben observe that the main body 
o( the cfaalk which surrounds Paris stretches from 
Tours to near Poitiers, (see the annexed map 
(Fig. 172.), in wUch the shaded part represents 
chalk.) 

Rfr 172. Between Poitiers and 

La Rochelle^ the space 



maiiced A on the map 
separates two regicms 
of dialk. This space 
is occujned by the odlite 
and certain other form- 
ations cdder dian the 
chalk, and has been 
supposed by M. £. 
de BeaumcMit to have 
formed an island in the 
cretaceous sea. South 
of this space we again 
meet with a formation 




which we at once recognize by its mineral cha- 
racter to be chalk, although there are some places 
where the rock becomes oolitic. The fossils also 
are upon the whole very similur, although some 
new forms now begin to appear in abundance 
which are rare or wholly unknown further to the 
north. Among these may be mentioned many 
Hippurites, Sphserulites, and other members of 
that great family of moUusca called Mudisies by 



a. XT.] IN sovTH OP «mop& 39S 

Lannrck, to whidi nothing analogous has been 
discovered in the Uring creation. Although verjr 
uncommon in England, one species of this &mi]^ 
has been discovered in our chalk. 




. Traoirene McaoD of part of tbe nil of the « 

DUgmfiHi to flbow the Btnicture^ 
. Vertictl Kdion of the mnr. 



On tbe ade when Ibe bI 
AuTOv and cocTGspoiiding 
but Ibej m usuail; lets proi 



Unnest, there u one titernal 
Hdge, a. b. Figs. l^S, 174. ; 
thu in these figun ■■■ This 



■peoei bai been referred to Hippurites, but does not, I UiJieTc, 
fbllj agree in character with that genus. I bave never seen tbe 
opercular |4ece^ or tu^, ai it u called by tboie coDcboIogists 
who r^ard tbe Saduta ai biralTe nutlliuca. 

But this Ikmilj, which is so fe^l; r^resented 

in England and the north of France, becomes 

qoite characteristic of rocks of the cretaceous era 

q2 



g^ DIFFEHBBXiCaJA&CtnS-O* {CHALK tTprt^ 

in tJWfl^uUi of JWkce, Sptim, Greece, , a4j4 Qthw 
eAuntrits' borderiBg- the Meditenwwan. 




Between tbe region of chalk last menttoaied in 
which Perigeux is situated, and the PyreneeB, 
the space B intervenes (see Map). 

Here die tertiary strata cover, and for the moet 
part conceal, the cretaceous rocks, except in some 
spots where they have been laid open to vi^w. by 
the denudation of the newer formations. In tlKse 
places they are seen still preserving the form of a 
white chalky rock, which is fUled in part with 
grains of green sand. Even as £ir south as Tercis, 
on the Adour, near Dax, it retains this character 
where I have examined it, and where M. Orate- 
loup has fomid in it Ananchytes omta (Fig. 158.), 
and other fossils of the En^sh chalks td^ther 



Oli.'it*;] ■''■■ ''ia"80«ira-»F"BUBt»ar-.r.(i ff^ 

Mdi' ^ppuritesi Wlien we am^ at Ba;»nn« 
and the Pjirenees, the cretaceous fbrdftiatimii. aJ^ 
thou^ still exhibiting some of the same niineralo- 
gical'peculiarities, b neverthelesg greatly changed. 
Its calcaieous divisioD consists fiir the most p^ui: of 
coihpact crystalline marble, often full of nummu- 
lites (see Fig. 180.}, and those portions which 
may be imagined to represent the green-sand, are 
composed of shales, grits, and micaceous sand- 
stone, containing impressions of marine plants, 
together with lignite and coaL Tliere are also 
beds of red sandstone and conglomerate belonging 
to the saiae group. These rocks ascend gradually 
into the highest parla of the Pyrenees, and cross 
over into Spain, where the cretaceous system as- 
sumes a character stiU more unlike that of northern 
Europe. 

Here, as on the north side of the Pyrenees, the 
most conspicuous fosfuls are hippurites, sphieru- 



iig. 18a 




a, !:|il<riia)iiuiWceofoneoftlienuinniuliUs,ofirhichlcn)gitudiRal 
en in the limettoru!. 
omrfnnw. 

Q 3 



342 DIFFERENT CHABACTES OF CHALK tPtttll. 

lites, and nummiilites. The last-mentioned ibssO, 
so called from its resemblance to a piece of money, 
is a genus of mollusca very abundant in the ter- 
tiary strata of Northern Europe; but only met 
with in chalk in the South of Europe. 

So many species and genera of shells now want- 
ing in our northern seas, are frequent in the 
Mediterranean, that we need not be surprised, 
when following from north to south the deposits 
of the old cretaceous sea, at finding similar modir 
fications in organic forms. 

The cretaceous rocks in the Alps, Italy, Greece, 
and Asia Minor, are distinct in like manner from 
the type of that formation in the North of Europe; 
yet their age in most of these countries can be 
cles^ly ascertained, partly by following them con- 
tinuously from the north in the manner above 
described ; and partly by their position below the 
tertiary, and above the oolitic strata. 

We learn from the researches of M. M. Boblaye 
and Virlet, that the cretaceous system in the 
Morea, is composed of compact and lithographic 
limestones of great thickness ; also of granular 
limestones, with jasper; and in some districts, as 
in Messenia, a puddingstone with a siliceous ce- 
ment more than 1600 feet in thickness, belongs 
to the same group.* 

* Bull, de la Soc Geol. de France, torn. Hi. p. 149. 



Ch.XYJ IN SOUTH OF SUROPE. 343 

It is evident, observe these geologists, from the 
great range of the hippurite and nummulite lime* 
stone, that the Soiith of Europe was occupied at 
the cretaceous period by an immense sea, which 
extended from the Atlantic Ocean into Asia, and 
comprehended the southernmost part of France, 
together with Spain, Sicily, part of Italy, and the 
Austrian Alps, Dalmatia, Albania, a portion of 
Syria, the isles of the iBgean, coasts of Thrace, 
and the Troad. 

In proportion, therefore, as we enlarge the 
sphere of our researches, we may find in the 
strata of one era, the mineralogical counterparts 
of the rocks, which, in a single country like Eng- 
land, may characterise successive periods. Thus, 
the grits, sandstone, and shale with coal, of the 
Pyrenees have actually been mistaken by skiliul 
miners for the ancient carboniferous group of 
England and France. In like manner the creta- 
ceous red marl and salt of northern Spain have 
been regarded as the same as our new red and 
saliferous sandstone; and the lithographic lime- 
stone of the Morea might be confounded with 
the oolite of Solenhofen in Germany. 

The beginner, perhaps, on hearing these facts, 
may object to the term cretaceous, as applied to 
the rocks of the southern region in which there is 
no chalk. But the term green-sand would have 
been equally inappropriate as a general name for 

Q 4 



^6 WEALDSN OROUF. CFtotll. 

To all these subdivisions, the conunon name of 
the Wealden has been given, because they may 
be best studied in part of Kent, Surrey, and Sus- 
sex, caDed the Weald. 

We have seen that the fossils of the chalk and 
green-sands which repose upon the Wealden are 
all marine, and the species numerous; and the 
same remark applies to the Portland stone and 
other members of the Oolitic series which lie im- 
mediately beneath (see Fig. 181.). But in the 

Fig. 181. 
( -• • -r ^ ^ jf A Chalk. 



manne 



=^^ ^""^ — -=g Weald clay, 1 

Areshwater^ -:.?:^iV;vf:^'- :<':-';• :>v a Hartings sand, I Wealden. 
^-^-T^'^^ ==^^^ Pim)eck bedi^ J 

marine I j Oolite. 

(L J 

PoH^on qf the Wealden between two marine JbrmaHoms, 

Wealden itself, although the fossils are abundant 
as to quantity, the number of different species is 
comparatively small, and by far the greater part of 
them show that they were deposited in a freshwater 
lake, or estuary communicating with the sea.* 

Fossils of the Wealden. — The shells of this form- 
ation are almost exclusively of fluviadle or la- 
custrine genera, such as Melanopsis, Paludina, 
Neritina, Cyclas, Unio, and others. The indi- 
viduals are sometimes in such provision, that the 

* Fhton, Geol. Trans, vol. iv. p. 104. Second Series. 



ch. XVI.J roBsiLS* , 347 

surface of each thin layer of marl or clay is covered 
with the valves of Cycla% and whole beds of lime- 
stone are almost entirely composed of Paludinae. 
Intermixed with these freshwater shells, there are 
a few which seem to mark the occasional presence 
of salt water, as for example, a species of Bulla, 
together with an Oyster, and the Exogyra, a 
genus of unimuscular bivalves allied to the oyster 
(see Fig. 182.). The conclusion to be drawn from 
the presence of a Corbula (see Fig. 183.) and 

Fig. 182. Fig. 183. 




EMggrali^aia, Httop. Corbula alata, Fittoo. 

Magnified. 

Mytilus is more doubtful ; for although these ge- 
nent are for the most part marine, still there is a 
Mytilus living in the Danube, and one species of 
Corbula inhabits the river La Plata, in South 
America, as well as the adjoining sea, while an- 
other is common to the Caspian, and the rivers 
Don and Wolga. But admitting all these to have 
been marine, they by no means outweigh the 
evidence, both of a positive and negative kind, de- 
rived from shells in favour of the freshwater ori- 
gin of the Wealden. In no part of this deposit 
do we meet with ammonites^ belemnites, terebra- 
tulse, corals, sea-urchins, or other testacea and 

Q 6 



zoophytes bo charactefiatic of the chalk above, or 
the botite' btlow the We^den. 
^ Shells of iJie Cypris, an animal allied to the 
CniilBcea, and . before mnidooed ^p. 6&.) as 
Fig. 184, Fig. 185. Hg. 186. ' 





abounding in lakes and ponds, are also plentifully 
scattered through the clays of the Wealden, B<»ne- 
Flg. 18T. times producing, like plates of 

mica, a thin lamination (see 
Fig. 187.). Similar cypriferoos 
marls are found in the lacus- 
trine tertiary beds of Auvetgne, 
and in recent deposits of shell marl. 

TTie fishes of the Wealden bdong partly to the 
genera Pycnodus and Hybodus, forms common to 
the Wealden and Oolite (see Fig. 225.) ; but the 
teeth and scales of a species of L^idotus are most 
widely diffused (see Fig. 188.). The general form 
of these fish was that of the carp tribe, attbongh 
perfectly distinct in anatomical character, and more 
allied to the pike. The whole body was covered 
with large rbomboidal scales very thick, and baviiig 
Ae exposed port covered with enamel. Most of 




i. ude Tiev of teeth. 



the species of this genus are supposed to have 
been either river fish, or inhabitants of the coasts, 
having not sufficient powers of swimming to ad- 
vance into the deep sea. 

Among the remains of vertebrata, those of rep- 
tiles form the most remarkable feature. Some of 
them belong to tortoises, such as the Trionyx and 
Emys, genera now occurring in freshwater in 
tropical r^ons. Of Saiuian hzsrds there are at 
least five genera ; the Crocodile, Plesiosaur, Me- 
galosaur, Iguanodon, and Hylseosaur. The Ignan- 
odon, of which the remains were first discovered 
by Mr. Mantell, was an herbivorous reptile, and 
was r^arded by Cuvier as more extraordinary 
than any with which he was acquainted ; for the 
teeth, though bearing a great analogy to the' 
modem Iguanas which now firequent the tro- 
pical woods of America and the West Indies, 
exhibit many striking and important differences 
(see Fig. 190.). It appears that they have been 



eiOfTF. CC^tttO. 



worn bj mastication ; whertes the <nrigtiiig her- 
biToroos reptiles clip and gnaw off the vegetable 
productions on which they feed, but do not diew 
dieoL Th^ teeth, when worn, present an an* 



Fig. 19a 

Fig. 189. 





CSrmra iff tooth £• 
aAUt^*Dom down, 

'^^a^'SL Poimiedioolk^ 

a poumg tautiuiL 



pearance of having been chipped off, and never, 
like the fossil teeth of the Iguanodon, have a flat 
ground sur&ce, (see Fig. 189.), resembling the 
grinders of herbivorous mammalia. From the 
large bones, found in great numbers near these 
teeth, and &irly presumed to belong to the same 
animal, it is computed that the entire length of 
this reptile could not have been less than seventy 
feet. 

The bones of birds of the order Grallas or 
waders have been discovered by Mr. Mantdl in 
the Wealden, and appear to be the oldest well- 
authenticated examples of fossils of this class 
hitherto found in Great Britain.* But no portion 

• Mantell, Proceedings Geol. Soc. vol. ii. p. «03. 



rossn, PLASTs. 



of the skeleton of a mammiferous quadruped has 
yet been met with. 

The vegetable remans, which are numerous, 
exhibit many characters of a tropical flora, some 
being allied to the living genera Cycas and Zamia 
(see Fig. 194.), others to large Equiseta. There 
are also Conlfene allied to Araucaria, and other 
genera of warm climates (see Fig. 191), besides 
numerous ferns (see Fig. 192,), 



Fig. 191, 



Fig. 193. 




leriigracau (FIttnn),J»i 
portion of (he same insgnifled. 



Passage of Wealden beneath Chalk. — It baa been 
already seen that the chalk and green sand have 
an aggregate thickness of 1000 or sometimes 1600 
feet. It is therefore a wonderful fact that after 
penetrating these rocks, we come down upon a 
subjacent fieshwater formation from 800 to 1000 
feet in thickness. The order of superposition is clear 
for we see the weald clay passing beneath tbe green- 
sand in various parts of Surrey, Kent, and Sussex ; 
and if we proceed from Sussex westward to the Vale 



mf. 



J. 



Kfr i». 



Ysle or Vrtaifianr. Wdta. 










,.- ,* 



of WaidoHT, we there again oboeire the sm^^ 
£^ffoia:riQn oocopyiiig the saiae relative poaiipoi^ 
nod restiag on the oolite (see Fig. 193.). Or if 
^fe pase fiom the base of the south downs in- Soft* 
8CX9 and cross to the Isle of Wi|^ we there 
again meet with the same s^es reappearing be- 
neath the green-sand, and we cannot donbt dial 
the beds are [M*oloi^ed subterraneouslj) as inr 
dicated by the dotted lines in Fig. 194* 



Fig. 194. 



Uto or Wight. 







— \^" 



It has been already suggested that, during the 
accumulation of the green-sand, there was a gradual 
sinking down and submersion of land, by which 
the wide open sea of the chalk was produced. But 
the position of the Weajden points still more 
forcibly to such a conclusion, and especially the 
appearances exhibited at the point of junction of 
the wealden, and the oolitic formation on which it 
rests. First, in regard to its junction with the 
superincumbent lower green-sand, »the beds of 



this last, says Dr. Fitton, depose in the south-east 
of 1 England, cpnfonnablj upon those of the sub-] 
jao ent -w ea id elay. There is no indieaticm <^ d»^ 
turbance : ^^ To all appearance the change from 
die deposition of the freshwater remains to that 
oT the marine shells, may have been effected 
sim^fy by a tranquil submersion of the land to a 
greater depth beneath the surface of the waters." * 
Portland dirt-bed and proofs of subsidence*''^ Hxxt 
when we examine the contact of the Purbeck beds, 
or infinar division of the wealden, with the Pbrt- 
land stone^ or upper memb^ of the oolite, some 
very singulis phenomena are obsarved. Between 
the two formations, the marine and the freshwater, 
there intervenes in Portland a layer c^ dark mat- 
t^, called by the quarrymen the ^^ Dirt,'* or 
^' Black dirt," which appears evidently to have 
been an ancient vegetable soil. It is from twelve 
to eighteen inches thick, is of a dark brown or 
black colour, and contains a large proportion of 
earthy lignite. Through it are dispersed rounded 
fragments of stone, from three to nine inches iii 
diameter, in such numbers that it almost deserves 
the name of gravel. Many silicified trunks of 
coniferous trees, and the remains of plants allied 
to the Zamia and Cycas are buried in this dirt- 
bed (see figure of living Zamia). 

* Oeol. of Hastings, p. 28 




Theee plants must have become fossil on the 
spots where they grew. Tlie stumps of the trees 
stand erect for a height of &om one to three feet, 
and even in one instance to six feet, with their 
roots attached to the soil at about the same £s- 
tances from one another as the trees in a modem 
forestf The carbonaceous matter u most abun- 
dant immediately around the stumps, and round 
the remfuns of fossil Gfcadem. X 

Besides the upright stumps above mentioned, 
the dirt-bed contains the stems of sihcified trees 
laid prostrate. These are paitij sunk into the 

• See Flindei'* Voyage. 

t Mr. Webster firat noticed the erect poeitioo of the trees 
and described the Kit-bed. The account here giyea ii 
drawn from Dr. Buckland and Mr. De ta Beche, Geo). 
Trans., Second Series, vol. iv. p. I. ; Hantell, GeoL of S. E. 
of Engjand. p. 336 ; and Dr. Fitton, Oeol. Tnuis., Second 
Series, voLiv. p. 880. 

X Ktton, ibid. pp. S20, 281. 



Ch. XVI.3 



IN ISI^ OF POKTLAND. 



35S 



black earth, and partlj enveloped by a calcareo- 
siliceous slate wfaicli covers the dirt-bed. The 
fragments of the prostrate trees are rarely more 
than three or four feet in length ; but by joining 
many of them together, trunks have been restored 
having a length from the root to the branches of 
from 20 to 23 feet, the stems being undivided 
for 17 or 20 feet, and then forked. The dia- 
meter of these near the roots is about one foot.* 
Root-shaped cavities were observed by Professor 
Henslow to descend from the bottom of the dirt- 
bed into the subjacent Portland stone, so that the 
uppermost beds of the Portland limestone, though 
now solid, were in a soft and penetrable state 
when the trees grew.f 

The thin layers of calcareous slate (Fig. 196.), 




ftftshvater calcaicouB 
slata 

dirt-bed and ancient 
forest 

marine Portland 
stone. 



Seetiou in Isle (tf Portland, DorieL (Bucklaod and De la Beche.) 

were evidently deposited tranquilly, and would 
have been horizontal* but for the protrusion of the 



* Fitton, QeoL Trans., Second Series, vol. iv. pp. 220, 22 1, 
t Buckland and De la Beche, GeoL Trans., Second 
Series, vol. iv. p. 16. 



356 ■•'' itmi. toKiHr ' - ' ([FWa 

•nmpe' of tbfe treCB, aroand t^ top of'bfidi 'tk 
iriiioh they fann betnis[^erical coQcretiboa.' '' 
^e dirt-bed is by no mettnd t»ttfined fe'flfi 
uAmA of Portland, but isseen in the-Bantfr fdalHe 
pontkm in a cliff east of LulworA OoTe,- iti 
Sonet^ffe, where, as the strata have been'fS*'' 
tiiriied, and are now inclined at an angle of 48", 
die stamps of the trees are also in<4ined'at thfe 
Rg. 197. 




ft«MwliiEWMMy£(KiHMta)Ku (Backlnnl m4 Dc la BhiIk.] 

same ang^e in an opposite direction — a beauUiiil 
- illiistration of a change in the position of hetfe 
ori^nally horizontal (see ^g. 197.). Traces of 
the dirt-bed have also been observed by Dr. 
Buckland, about two miles north of lliame, in Ox- 
fordshire ; and by Dr. Fitton, in the cliffs of the 
Boulonnois, on the French coast : but, as might be 
expected, this freshwater deposit is of limited ex- 
tent when compared to most marine formations. 

From the iacts above described, we may,^^, 
£rst, that the superior beds of the^oolitc^ whicdi ajcr 
fiill of marine shells, became dry knd, KoA oo:Veted 



fSkf,^Yl.2 IN |ff« .QFtP$!AVLANn 35g 

j^ ^Jhj^ef^ |Jbg?oug)io|it a porticii) of Ae t^^ae^mow 
occupiefl,by the south of En^iand^tbe jclhnate 
l^fiinf^ such as to admit the growth of the samia 
^|i4. f^yca^ 2dly. This land at l^figth iiaBk d<omn 
ffkd ,wQa^ submerged with its for^^ beiieath ^ 
b^y of freshwater,. from which »edimeut:^iyelopi- 
ii!^ fli^viatile shells was deposited* , Sdly. ^^ Tbf^ 
j^ifgular a^d uniform preservation of this thin bed 
of black earth over a distance of many miles, 
shows that the change from dry land to the stat^ 
of a freshwater lake or estuary, was not accom- 
panied by any violent denudation, or rush of 
water, since the loose black earth, together with 
the trees which lay prostrate on its surface, must 
inevitably have been swept away had any such 
violent catastrophe then taken place." * 

The dirt-bed has been described above in its 
most simple form, but in some sections the ap- 
pearances are more complicated. The forest of 
the dirtpbed waa not everywhere the first vegeta^ 
tion which grew in this region. Two other, beds 
of carbonaceous clay, one of them containiug 
Cycadem in an upright position have been found 
below itf, which implies other oscillations in the 
level of the same ground, and its alternate occu- 
pation by land and water more than once. There 

' * Buckland and De la Beche, Geol. Trans., Second 
^Series, vol. hr. p. 16. 

t FUton, Gool. Traos., Second JScriesi yolL m p. fSA^ 



358 WEALDEN STRATA [Pnt II. 

must have been, first, the sea in which the corals 
and shells of the oolite grew; th^i, land, which sup- 
pcMTted a vegetaUe soil with Cycadeae; then, a li^e 
or estuary, in which freshwater strata were dqx)- 
sited; then, again, land, on which other Cjcadees 
and a forest of dicotyledonous trees flourished; 
then, a second submergence under freshwater, in 
which the wealden strata were gradually formed; 
and, finally, in the cretaceous period, a return over 
the same space of the ocean. 

To ims^ine such a series of events will appear 
extravagant and visionary to some who are not 
aware that similar changes occur in the ordinary 
course of nature ; and that large areas near the 
sea are now subject to be laid dry, and then sub~ 
merged, after remaining years covered with houses 
and trees.* 

In some of these modern revolutions, such as 
have been witnessed in the delta of the Indus, 
in Cutch, we have instances of land being per- 
manently laid under the waters, both of the river 
and the sea, without the soil and its shrubs being 
swept away ; but such preservation of an ancient 
soil must be a rare exception to the general rule, 
for it would be destroyed by denuding waves and 
currents, unless the land sank suddenly down to 

* For an account of recent movements of land attended 
by such consequences, see Principles of Geology, Index, 
« Cutch," " Sindree," &c. 



eiuXVIJ FORMED IN SHALLOW WATER. 359 



m 

a great depth, or unless its form was such as to 
exclude the free ingress of the sea. 

Notwithstanding the enormous thickness of the 
wealden, exceeding in some places perhaps 1000 
feet, there are many grounds for believing that 
the whole of it was a deposit in water of moderate 
depth, and often extremely shallow. This idea 
may seem startling at first, yet such would be the 
natural consequence of a gradual and continuous 
sinking of the ground in an estuary or bay, into 
which a great river discharged its turbid waters. 
By each foot of subsidence, the fundamental rock, 
such as the Portland oolite, would be depressed 
one foot farther from the surface of the ocean ; but 
the bay would not be deepened, if new strata of 
mud and sand should raise the bottom one foot. 
On the contrary, such sand and mud might be 
frequently laid dry at low water, or overgrown for 
a season by a vegetation proper to marshes. At 
different heights in the Hastings Sand in the 
middle of the Wealden, we find again and again 
slabs of sandstone with a strong ripple-mark, and 
between these slabs beds of clay many yards thick. 
In some places, as at Stammerham, near Horsham, 
there are indications of this clay having been ex- 
posed so as to dry and crack before the next layer 
was thrown down upon it. The open cracks in 
the clay have served as moulds, of which casts 
have been taken in relief, and which are, there- 



SM WIALDKH flROCP. [FHIU. 

ftir^ leen on the lower surface of the skudston? * 
(■ee Fijf. Wa). 

Rj. 198. 




Near the same place a reddish sandstone occurs 
in which are innumerable traces of a fossil vege- 
table, apparently Sphenopteris, the stems and 
branches of whidi are disposed as if the plants 
were standing erect on the spot where they OTigi- 
nally grew, tlie sand having been gecdy de- 
posited upon aad aromid them ; and similar 
appearances have been remarked in other places 
in this fonnation. f In the same division also oS 
the wealden, at Cuckiield, is a bed of gravel os 
conglomerate, consisting of water-worn pebUes ^ 
quartz and jasper, with rolled bones of reptiles. 

• Obwnred b; Mr. Hantell and nifself in 1831. 
t Hutell, Oeol. of a E. of Englaad, p. SM. 



'{liese must hav^ been drifted by a ^yr^y^ m^ 
bably in water of no great depth. - .. .; 

The occasional presence of oysters in the Pur- 
beck limestone, and throughout the Hastings sand 
and Weald d^y^ proves, that the wat^s of the sea 
sometimes found accessiiito the estuary*, whether 
in consequence of subsidence, or in seasons when 
the body, of freshwater was lessened in volume. 

Geographical extent. — The Wealden strata have 
been traced about 200 English miles from west 
to east, from Lulwdrth Cove to near Boulogne^ in 
France^ and about 220 miles from north-west to 
south-east, from Whitchurch, in Buckinghamshire, 
to Beauvais, in France. If the formation be 
continuous throughout this space, which is very 
doubtfol, it does not follow that the whole was 
awtemporaneous ; because in all likelihood the 
phyacal geography of the r^on underwent fre<^ 
quent change throughout the whole period, and 
the estuary may have altered its form, and even 
shifted its place. Yet some modem deltas are of 
vaal; size, as for example, that of the newly disco*- 
vered Quorra, or Niger, in Africa, which stretches 
into the intaior for more .than 170 miles, and oc« 
cufHea^ it is supposed, a spac^ of more than 800 
males along the coast; dnis forming a surface of 

* Fitton, Geol. Trans., 2d Ser., voLiv. p. 32h 



OBIOIV 6F t^tatn. 

more than 25,000 square miles, or equal to about 
caie half of Englaad.* 

I have stated that the Wealden has been ob- 
served near Beauvais, in France ; and the locality 
is marked in the section at p. 315. It is called 
^ the country of Bray;" and resembles in struc- 
ture the English Weald between the north and 
south downs. In a similar manner the green- 
sand crops out from beneath the chalk, and fresh- 
water strata from beneath the greennsand. C^ 
member of the series, a fine whitish sand, contains 
impressions of ferns, considered by M. Adolphe 
Brongniart as identical with Lanckopteris MantdUj 
a plant found frequently in the Wealden. I ex* 
amined part of the valley of Bray in company 
with M. Gfraves, m Iddd, mid I observed that 
the sand last mentioned, with its v^etable re- 
mains, was intercalated between two sets of marine 
strata, containing trigoniae, and referred hy French 
geologists to the lower green-sand. In the same 
country of Bray, and associated with the same 
formation, is a limestone resembling the Purbeck 
marble, and containing a Paludina which seons 
specifically identical with that of Purbedc. 

If it be asked where the ccmtinent was placed 
from the ruins <^ which the Wealden strata were 



* Fitton, Geol. of Hastings, p. 66. ; wko oites Lander's 
Travels. 



Cb.XVI.] W£A£J>BN OfiOUP; 3^ 

derived, and by the dcainage of which a great 
river was fed, we are half tempted to speculate osi 
the former ^stence of the Atlantis oi Plato* 
The story of the submergence of an ancient con- 
tinent» however fabulous in history, may he true 
as a geological event. Its disappearance may have 
been gradual; and we need not suppose that the 
rate of subsidence was hastened at the period 
when the displacement of a great body of fresh- 
water by the cretaceous sea took place. Suppose 
the mean height of the land drained by the river 
of the Wealden estuary to have been no more 
than 800 or 1000 feet.; in that case, all except the 
tops of the mountains would be covered as soon 
as the fundamental oolite and the dirt"-bed were 
sunk down about 1000 feet below the level which 
they occupied when the forest before-mentioned 
was growing. Towards the close of the period of 
this subsidence, both the sea would encroach and 
the river diminish in volume more rapidly ; yet in 
such a mann^, that we may easily conceive the 
sediment at first washed into the advahcing sea to 
have resembled that previously deposited by the 
river in the estuary. In fact, the upper beds of 
the Wealden, and the inferior strata of the lower 
gteen-sand, are not only conformable, but of simi- 
lar mineral composition. 

It is also a remarkable foct, that the same Iffuano-' 
don ManidK which is so conspicuous a fossil in the 

R 2 



^04 BELATIVE AO£ OF [PaxtU 

Wealdkny bas recently been discovered near Maidr 
slone, in the overlying Kentish rag, or marine lime- 
stone of the lower green-sand. Hence we may 
infer that some of the saiirians which inhaUt^ 
the country of the great river, continued to live 
when part of the country had become submerged 
beneath the sea. Thus, in our own times^ we 
may suppose the bones of large alligators to be 
frequently entombed in recent freshwater strata 
in the delta of the Ganges. But if part of that 
delta should sink down so as to be covered by 
the sea, marine formations might begin to accu^ 
mulate in the same space where freshwater beds 
had previously been formed ; and yet the Ganges 
might still pour down its turbid waters in the 
same direction, and carry the carcasses of the 
same* species of alligator to the sea, in which case 
their bones might be included in marine as well 
as in subjacent freshwater strata. 

Ag^ of the WeaJden. — Some geologists have 
classed the Wealden as a member of the creta-» 
ceous group, while others have considered it as 
more nearly connected with the antecedent oolitic 
deposits ; nor is it easy to decide which opinion is 
preferable, because the organic remains of the 
cretaceous and oolitic groups are marine, while 
those of the interposed Wealden are almost all 
freshwater. The testacea and plants of the latter 
appear as yet to be specifically distinct from lliose 



Oli.XVR3 THE WEALDEN- OR^tJP. gflg 

of ally other formation; but if we examine the 
reptiles, it appears that the MegcHosawrui Buek^ 
hmdi is common to the Oolite and Wealden, the 
teeth and bones of this great saurian occurring 
both in the limestone of Stonesfield and in th^ 
Hastings sand. 

There are also some generic forms, both of rep- 
tHes and fish, common to the Oolite and Wealden, 
and not yet discovered in the Chalk. Vertebrae, 
tofr example, of the Plesiosaurus are not confined 
to the oolite and lias, but have been also found in 
the Wealden; and the Lepidotus, a genus of fish 
very clmracteristic of the Wealden, is unknown in 
the cretaceous group, while it is abimdant in the 
oofitic series. 

On the other hand, the same species of Igutoo^ 
don has been already mentioned as decidedly com-* 
mon to the Wealden and green-sand. 

In Scotland, and in different parts of the Con- 
tinent, marine deposits have been found which 
are supposed to have been coeval with the 'Weal- 
den, and which are intermediate in fossil eharae-* 
ters as in position between the Cretaceous and 
Oolitic systems.* They may have been contem- 
poraneous deltas of other rivers flowing froih the 
same ancient continent. 

Absence of mammalia. — Among the numerous 

♦ See Fitton, Geol. Trans., Second Series, vol. iv. p. 328,, 
and his references. 

R 3 



366 ABSENCE (WMAMMALTA [Part If . 

fossils of the Wealden, no remains of mamnialia, 
have been hitherto detected ; whereas we should 
naturally expect, on examining the deposits re- 
cently formed at the mouths of the €)oorra, Indf», 
or Ganges, to find, not only the bones oi birds 
and of amphibious and land reptiles, but also 
those of such warm-blooded quadrupeds as fre- 
quent the banks of rivers, or, like the hippopotamus, 
inhabit their waters. Would not the same current 
of water which drifted down and rolled the bones 
of the lizards, tortoises, and fish of the Wealden, 
have also swept down into the delta some frag^ 
itoents at least of mammiferous bones, had any 
animals of the highest class been then m exist- 
ence? As a general rule, indeed, we cannot lay 
miich stress on mere negative evidence; and it 
may he well to notice, that although so many 
teeth of the Iguanodon have been collected, it is 
only of late that a single small portion of a jaw of 
cme of these gigantic lizards was obtained Per- 
haps, in like manner, some bone or tooth of a fossil 
quadruped will one day be found. We may at 
least say, that we have at present no example of 
a continent covered with a luxuriant vegetati<A, 
and forests inhabited by large saurians, both aqua- 
tic and terrestrial, and by birds, yet at the same 
time entirely destitute of warm-blooded qua- 
drupeds. The nearest analogy to this state of 
things is that of New Zealand; and this fiu^t 



Cb.XVlO IN THE WEAU)£N. 3^7 

will be more particularly alluded to in the sequeL 
(See p. 442.) 

In conclusion I may remark, that from the 
time of the commencement of the Wealden, to far 
on in the Cretaceous period, we have signs of sub- 
sidence, and consequent diminution of land. But 
after the chalk was formed, or during the tertiary 
periods, we have, on the contrary, proofs of an in- 
crease of land in Europe. But we must not ex- 
tend these generalizations to the whole sur&ce of 
the globe; for other large areas may have been 
growing more and more continental during the 
cretaceous, and more and more oceanic during 
the tertiary periods, the direction of the prevail- 
ing subterranean movement being reversed. 



R 4 



368 



CHAPTER XVIL 



OOLITE ANJP LIAS. 



SubdiviskMis of the Oolitic group*— > Fossil shdk — Corals 
in the calcareous divisions only — Buried forest of Encri- 
nites in Bradford clay — Changes in organic life during 
accumulation of Oolkes — Characteristic fosnls — Signs 

. o£ neighbouring land and shoals — Supposed cetacea id 
Oolite. — Oolite of Yorkshire and Scotland. 



Oolite.— ^ Below the freshwater group last de- 
scribed, or, where this is wanting, immediately, 
beneath the Cretaceous formation, a great series 
of marine strata, commonly called " the Oolite," oc- 
curs in many parts of Europe. This group has been 
so named, because, in England and other places 
where it was first examined, the limestones bdong* 
ing to it had an oolitic structure (see p. 29.)* 
These rocks occupy in England a zone which is 
nearly thirty miles in average breadth, and ex- 
tends across the island, from Yorkshire on the 
north-east, to Dorsetshire on the south-west.* 
Their mineral characters are not uniform through- 
out this region; but the following are the names 

* For details respecting this formation in England^ see 
Oonybeare and Phillips's Geology, chap. iiL 



cai. xni.] DIVISIONS pF .the oolite. 369 

of the principal subdivisions observed in the cen- 
tral and south-eastern parts of England : — 



Upper {^ 



OOLITE. 

Portland stone and sand. 
Kimmeridge clay. 

Middle ('=• ^'f?^: 

L d, Oxford clay. 

re. Combrash and Forest Marble. 
Xjower-j yr Great Oolite and base of FuHers* earth. 
L^. Inferior Oolite. 

Tfae LiaB then succeeds to the Inferior Oolite. 



. The upper oolitic system o£ the above Table 
has usually the Kimmeridge day for its base, and 
the middle oolitic system the Oxford clay. The 
lower system reposes on the Lias, an argillo-cal- 
oaireous formation, which some include in the lower 
oolite, but which will be treated of separately in 
the next chapter. Many of these subdivisions are 
distinguished by peculiar organic remains; and 
tliough varying in thickness, may be traced in 
certain directions for great distances, especially if 
we compare the part of England to which the 
above-mentioned type refers with the north-west 
o£ France, and the Jura mountains, which separate 
that country from Switzerland, and in which, 
thoi:^h distant above 400 geographical miles, the 
analogy to the English type above mentioned isr 
iBore perfect than in Yorkshire or Normandy. 

To enter upon a systematic description of this 
oamplicated serieis of strata would require mafiy 

R 5 



S70 OOLITE enacr, tf^ti. 

chapters; the following frcts^ Atereiore, are seated 
from a mtiltitude of others, wifh a view of ilhis- 
trating the origin of the oolitic rocks, and of 
showing the state of organic life and geographical 
condition of part of the globe when they were 
formed. 

In almost all the minor divisions enmnerated in 
the above Table, Ammonites and Belemnites are 
found (see Figs. 213. 215.), but of species difierent 
from those of the cretaceous period. The ammo- 
nites are of various sizes, from the size of a small 
carriage-wheel to less than an inch diameter. 

It is not uncommon to find belemmtes in dif- 
ferent members of the series, "^itb full grown ser-* 
pulfie attached to them. As these diells, like tbe 
bone of the cuttle-fish, so o£ben thrown on our 
shores, were internal, it is dear, that afia&r the 
death of the cephalopod the belemnite remaizied 
for some time unburied at the bottom of the sea, 
so that the serpulse grew upon it. 

These cephalopoda, swimming about in the opm 
sea, left their shells to be imbedded iitdifferently 
in whatever sediment was then in .the coiHse of 
^deposition, whether calcareous or argillaceous^ But 
the corals are almost entirely confined to the lime- 
stones, and are wanting in' tbe dense fi>rmalio]|8 of 
interposed clay, as also in: the llas^ these Koopkyles 
requiring, not only carbonate of Hme So» tlieir 
support, and clear water, but a bottom nanninii^ 



Ch.X*TL] PO««IL CORAU. gjl 

ftor years imcliang«<^ eitber by the shifung of sand 
or the accession of firesh sediment. 

In the Upper Oolite of England, corala are 
rare, although one species is found plentiAiUj at 
Tisbury, in WQtshire, in the Portland sand, con- 
verted into flint and chert, the original calcar»>us 
matter being replaced by silex. (Fig. 199.) One of 
the limestonea of the Middle Oolite has been called 
the " Coral Rag," because it consists, in part, of 
continuous beds of petrified corals, for the most 
part ret^ning the position in which they grew at 
the bottom of the sea. They belong chiefly to the 
genera Caryophyllia {Fig. 200.), Agaricia, and 
Pig. $00. 

Tig. 199. 




w oWoKO, Blulnv Carvl^sima "■•n'*i™, P.rklR 

Dplp« OdUr.nibarT. c«J rij, Steepln Aihura. 

Astrea, and sometimes form masses of coral fifteen 
fbe« thick. These coralline strata extend through 
die ealcaieous hills of the N. W. of Berkshire, 
md: north of Wilts, and again recur in Yorkshire, 
s 6 



Qg^; OOBAW OF OOLNS. lirMtlk* 

near Scarborough. Akhough the name of coral 
rag has been thus appropriated, there are pctftiona 
of the }ower oolite, as &>r exaiD|de tiie Grieat and 
Inferior Oolite (/ ff. Table, p. 369.). which are 
equally entitled in many places to be called con4- 
line limestones. Thus the Great Oolite near 
Bath contains various corals, amoog which tbp 
EttHomia radiata (Fig. 201.) is very conspicaooa^ 

fig 901 




o the tubes. 

b. vertiCHl section, Bhowing tbe ndiMion of tbe tobei. 

c. portion ofinterior of tubes magmGed, bhawing (triBUd nuJiM. 

single individuals forming masses several feet in 
diameter ; and having probably required, like the 
large existing brain-coral (Meandrina) of the tro- 
pics, many centuries before their growth was 
completed. 

Different species of Crinoideans, or ston&4ilie8] 
ace also common in . the same rocks with corala; 
and, like them, must have enjoyed a firm bottom, 
vh&K their root^ or base of attachment, renHuned 
undisturbed for years (c Fig. 202.) Such bauia. 



Ch.tFM} 



9BAlMrMB fiS^Cftkll^iO. 



^' 



Bg. fi02« 







Jpiocrinitesrohmdu9,crPearEnerinitei Miller. Fouil at Bradford, Wilts. 

a. Stem of Apiocrinitea, and one of the articulations, natural size. 

b. Section at Bradlbrd of great oolite and Qiverlymg clay, ofo- 

taining the fossil encrinites. See text 

c. Three perfect individuals of the Apiocrinite, represented as 

they grevr on the surface of the Great O^ite. 
4, Body of the Apiocrinites rotundtu^ 

tharefore, are alinost confined to the limestones ; 
but an exception occurs at Bradford, near 3ath, 
where they are enveloped in clay* In this cafley 
however, it appears that the solid uppef surface 
of the " Great Oolite " had supported, for a time, 
a thick submarine forest of these beautiful zoo- 
phytes^ imtil the clear and still water was invaded 
by a current charged with mud, which threw 
down the stone-lilies, and broke most of their 
stems short off near the point of attachment. The 
stumps still remain in their original position; but 
the numerous articulations once composing the 
stem, arms, and body of the zoophyte, were scat- 
tered at random through the argillaceous deposit 
in which some of them now lie prostrate. Iliese 



974 BSAMtMfli EMlmmM. tTMIt. 

appearances are represented in the Bection b. Fig. 
202., where the darker strata represent the Brad- 
ford clay, a member of the Forest marble (e. Table, 
p. 369.). The upper surface of the calcareooa 
stone below is completely incrusted over with a 
CK)ndnuous pavement, formed by the stony roots 
or attachments of the Crinoidea ; and besides this 
evidence of the length of time they had lived on 
the spot, we find great numbers of single ver- 
tebree, or circular plates of the stem and body of 
the encrinite, covered over with serpulffi. Now 
these serpulse could only have begun to grow after 
the death of swne of the stone-lilies, parts of 
whose skeletons had been strewed over the floor 
of the ocean before the irruption of argillaceoas 
Bud. In some instances we 6nd that, after the 
paraside serpulse were full grown, they had be* 
Fig. ao3. 




0. Siagle vettvlm, or articulation of an Encrinlle oTergroWD with 

•erpuhe and corals. Natural •ire. BiBdrord clay. 
t. Portion of the same magnified, ihowing the coral Beraueea 

iBbaiana covering one of tbe MrputtE. 



cft.xinL3 fscuuar vomniA $75 

eosne incmsted orer with a ooral^ called Bermieea 
dUwriana ; waA many generations of these polyps 
hud liucceeded each other in the pure water before 
tliey became fossiL 

We may, therefore^ perceive distinctly that^ as 
the pines and cycadeons plants of the ancient 
Portland Forest were killed by submergence 
vmdsx firesh water, and soon buried under muddy 
sediment, sd an invasion of argillaceous matter 
put a sudden stop to the growth of the Bradford 
Encrinites, and led to their preservation in marine 
strata^* 

Such diflTerences in the fossils as distinguish the 
calcareous and argilJbceoos deposits from each 
other^ would be described by naturalists as arising 
out of a difference in the stations of species ; but 
besides these^ there are variations in the fossils of 
the higher, middle, and lower part of the oolitic 
series, which must be ascribed to that great law 
of change in organic life by which distinct assem- 
blages of species have been adapted, at successive 
geological periods, to the varying conditions of the 
habitable surface. In a single district it is diffi- 
cult to decide how far the limitation of species to 
certain minor formations has been due to the 
local influence of stations, or how far it has been 
caused by time, or the creative and destroying 

* For a fuller account of these Encrinites^ see Buckland's 
Bridgeivater Treattse, vol. i. p. 429. 



3ZS roasiLS or [m il 

kw above aUudefl to. But we req<^oize. the 
reality. «f die last loeetioned infliiience, whea 
we contrast the whole oolitic aeries. of England 
with tbat of partB <^ die Jura, Alpe, uid other 
distant regicHis, where there is scarcely any litbo- 
logical retemblance ; aod yet some of the same 
fixsils jUHti in peculiar in each conntry to the 
Uppo', MidtUe, and Lower Oolite formations re- 
ipeclively. Mr. Thnrmatm has shown how remark- 
ably this fact holds true in the Bernese Jura, 
although the argillaceous divisions, so conspicuous 
in England, are feebly represented, and some en- 
tirely wanting. 

Amongst the <diaracteristic fossils of the Upper 
Oohte, may be mentioned the Ottrea dtUoidta 
(Fig. 206.), found in the Kimmeridge clay through- 
out England and the north of France, and also in 
Scotland, near Brora. The Gryphaa viryula (Fig. 

FOSSILS OF THE OOLITE. 

Kg. 906. 








204.), also met with in Ae same clay near Ox- 
ford, and so abundant in the upper oolite of parts 
of France as to have caused the deposit to be 
termed - ** mantes it gryphees viigule." Near 
Clermont, in Ai^nne, a few leagues &oin St. 
Meaehonld, these uidurated marls crop out from 
beneath die gault; and, on decomposing, leave 
the surface of every ploughed iield lit^fdlj strewed 
over with fossil oysters. 



379 ooLm Boup. rxMU- 

One of the limestones of the Jura, referred to 
the age of the English coral rag, has been called 
** Nerinaean limestone'' (Calcaire a N^rinees) by 
M. Thirria; Nerirusa being an extinct genus of 
univalve shells, much resembling the Cerithium 
in external form, and peculiar to the oolitic 
period. The annexed section (Fig, 207.) shows 
the curious form of the hollow part of each whorl, 
and also the perforation which passes up the 
middle of the ccdumella. N. GoodkaOit (Fig. 
208.) is another English species of the same 
genus, from a formation which seems to form a 
passage from the Kimmeridge clay to the coral 
rag.* 

A division of the oolite in the Alps, regarded 
by most geologists as coeval with the English 
coral rag, has been often named *^ Calcaire a Di- 
cerates," or " Diceras limestone," from its con- 
taining abimdantly a bivalve shell (see Kg. 209.) 
of a genus allied to the Chama. 

Among the (^oracteifistic shells of the Inf<^or 
Oolil^, I may instance Terdmxhda qmosa (Fig* 
ail.), Pkoiadamya Jidiada (Fig. 212.), Belemtiites 
hadalus (Fig. 218.), aod Terebrat^da digmd (Fig. 
216.) 

Aa iUustraticMis of sheila having a greair vfert k tf 
range, I may allude to Trigmia ffMosa (Fig. 

♦ Fitton, GeoL Trans., Second Series, vol. iv. pl.«3. fig. 12. 




20,5,)* which abounds In the Portland stone of 
V^tshire, and the Inferior Oolite of Yorkshire. * 
Also Oxirea MarihU (Fig. 217.), common to the 

* See Williiuiisoii, Proceedioga Oeol. Soc. No. 47. 



OOCm OR4M7F. fAstlf. 

Qnnbnirii of Wilts and the Inferior Oolite of 
Yorfcahiie ; and, lastly, Orttada refiexa {Fig. 214.) 
and Ammamtet striatuhis (Fig. 215.), fiissils cobgk 
mon to the Inferior Oolite and Lias. 

Sndi facts by no means invalidate the general 
rule^ that certain fessils are good chronological 
tests of geological periods; but they serre to- 
caution us against attaching too much importance 
to single species, some of which may have a 
wider, odiers a more confined vertical range. We 
have before seen that, in some of the tertiaiy 
formations, some species occur both in the older 
and newer groups, yet these groups may be dis- 
tinguishable fix>m one another by a comparison of 
the whole assemblage of fossil shells proper to 
each. 

SiffTU of neighbouring land and shoals. — The 
corals and shells above alluded to, and the fish, 
Crustacea, and odier accompanying fossils, suffi- 
ciently attest the marine origin of the oolitic strata 
in general. Yet there are fi-equent signs of 
shallow water and of neighbouring land; and 
these are the more worthy of attention, as they by 
no means diminish as we proceed downwards to 
the inferior parts of the oolitic series. Had the 
bottom of the sea in Europe been unmoved during 
the entire oolitic period, the first, or oldest beds of 
the oolite, 'must have been accumulated in' the 
deepest water, the middle oolite in water of less 



Gb.XVU.] SIGNS OF LAtf0l 99|. 

depths And the upper in the shiillciweftt of alL 
The appearanoea about to be described militate 
against this condusion* The Kimmeridge claj^ 
in the Upper Oolite, consists, in great part, of a 
bitUBiinous shale^ sometimes forming an impure 
ooal several hundred feet in thiekness. < In some 
places in Wiltshire it much resembles peat ; and 
the bituminous matter may have been, in part at 
least, derived from the decomposition of vege- 
tables. But as impressions of plants axe rare in 
these shales, which contain ammonites, oysters, 
and other marine shells, the bitumen may perhaps 
be of animal origin. The occurrence, however, of 
fossil wood in the Upper Oolite shows that there 
were then lands from which plants were drifted 
into the sea. 

The celebrated lithographic stone of Solen- 
hofen, in Bavaria, belongs to one of the upper 
divisions of the oolite, and affords a remarkable 
example of the variety of fossils which may bd 
preserved under favourable circumstances, and 
what delicate impressions of the tender parts of 
certain animals and plants may be retained where 
the sediment is of extreme fineness. Although 
the number of testacea in this slate is small, and • 
the plants few, and those all marine. Count Mun* 
ster had determined no less than 287 spedes of 
fossils when I saw hia collection . in 1833; and 
among them no less than seven species of &jmg 



Uzardh or pterodaetyls, six muirjaps, tbroe lor* 
toueO} sixty species of fish, ibrty-»6ix of ^rustaoet) 
and twenty^six of insects. These inseels, amo^g 
which is a libellula, or dragoB-fly, must ham 
been blown out to sea, probably from tibier same 
laad to which the flying lizards, aad otiber osi»* 
temporaneous reptiles, resorted. 

In one of the upper members of the h^krwr 
Oolite of England the ripple-^aoark is distinccly 
aeen throughout a considerable thickness of thin 
fissile beds of a coarsely oolitic limestone. The 
rippled slabs are used for roofing, and have been 
traced over a broad band of country from Brad*- 
ford, in Wilts, to Tetbury in Gloucestershire. 
These calcareous slabs, or tilenstones, are separated 
from each other by thin seams of day, which 
have been deposited upon them, and have taken 
their form, preserving the undulating ridges and 
furrows of the sand in sudi complete int^rily, 
that the impressions of small footsteps, appa- 
rently of crabs, which walked over the soft wet 
sands, are still visible. In the same stone the 
olaws of crabs, fragments of echini, broken shells, 
pieces of drift wood, and other signs of a neigh- 
bouring beach, are observed. 

The slate of Stonesfield has lately been shown 
by Mr. Lonsdale to lie at the base of the Inferior 
Oolite. It is an oolitic shelly limestone, only six 
feet thick, but very rich in organic remains. It 




Oh.XVIL] STOHBOniliD BhATS, Qgg 

ooataBOS sooie pebbles of a rook very similar to 
kse^ and with tkem the fossil remains of belem- 
sites, trigonise, and other marine shells. Besides 
fragments of wood, which occur in aU parts of the 
oolitic group, there are many impressions of ferns^ 
Fig. SIS. eycadeae, and other terrestrial plants. 
Several insects also, and among the 
rest, the wing-covers of beetles, are 
perfectly preserved (see Fig. 218.), some 
of them approaching nearly to the genus 
Buprestis.* The remains, also, of many 
genera of reptiles, such as Plesiosaurus, 
s^nmqf Crocodile, and Pterodactyl, have been 

Btipretti$i 

stooetfidkL discovered in the same limestone ; and, 
what is still more remarkable, the jaws of at 
least two species of mammiferous quadrupeds, 
allied to the Didelphys, or opossum. These fos- 
sils afPord the only example yet known of terres- 
trial mammalia in rocks of a date anterior to the 
Eocene period. 

This exception is the more deserving of notice, 
because even no cetacea have as yet been observed in 
any secondary strata, although certain bones, from 
the great oolite of Enstone, near Woodstock, in 
Oxfordshire, have been cited, on the authority of 
Cuvier, as referable to this class. Dr. Buckland, 
who has stated this in his late Bridgewater Trea- 

* See Buckiand's Bridgewater Treatise. 



tiK'*,hub{td.lhie kandMsi to wsmI'MB .^K^flfafF 
posed idaa -al a whale, in ofdcrt^ttiMc^OMt^ 
iB^lfat examine into iti clainu to be eoiu)d»«d'«4 
cetaceons. It ia tbe c^inioa of diat eminent -«Mfr^ 

parative anatomist, that it cannot bave bdoi^^ 
to the cetacea, because the £ae-am in tbeee inaiiHij 
mfmrnftlin is invariably mach flatter, and d«Mid<rf 
all muscular depressions and ridgea, one vf whicb 
ie BO prominent in the middle of this bone (see Fig. 
219.). In aaurians, on the contraiy, euch ridg^ 
Kb- sis. 




exist for the attachment of muscles ; and to some 
tinimal of that class the bone b probably referable. 
Oolite of Yorkshire and Scotland. — North of the 
Humber, in Yorkshire, the Inferior Oolite assumes 
a form very different from that which distinguishes 
it in the south. It may there be called a coal 
formation, as it contains much v^etable matter, 

• Vol.!. p. lis. 



4i.4mu -*' .^.ao&m^ 



aiAooal) kuetsmitified witli sand and sandBtoiws; 
!I%e)iigli stale of preservation and number of the 
plaiits reader it probable that land was not &r 
ciMlant The dame may be said of the oolitic 
(i9a1 of Bron9» on the southeast coast of Suther** 
teiwifthjre, in Scotland, where the In£^riar Oolite 
W^Sssmm ooaU ene bed of which is d§ feet m 
thickness. The plants resemble those in the York- 
shire oolite^ and a great number of the associated 
marine shells and other fossils are the same * ; 
but the mineral characters of the sandstone, shale, 
and calcai^eous grit, differ considerably. 

« MTiirchison, Geol, Trans., vol. ii. Second Series. 



8 



CHAPTER XVm. 

OOtlTB AND LIAS wftliirrf. 

IfiDvai chanctcr of Lim — Nvneof Gryphitelimeatone— 
Fosdl ftsh — IchUifodofulites — Reptiles of the Liaa — 
IchthjosBur and Plesiosaur — Newlj-discoTered inaiiiie 
Reptile of the Oali^Mgoa bUads — Saddm death and 
burial of fossil nninni* in LiM — Ori^ of the Ocdite 
and Liaa, and of altenatiiig cakareoiu and argillaceoui 
fonnatioiH — Phjiical geography — Vales of clay — HiUt 
and eacarpmeDts of limestone. 

Lias. The English provincial name of Lias has 
been veiy generally adopted for a formation of 
argillaceous limestone, marl, and clay, which 
forms the base of the oolite, and is classed by 
many geologists as part of that group. They pass, 
indeed, into each other in some places, as near 
Bath, a sandy marl called the marlstone of the Lias 
being interposed, and partaking of the min^^ 
characters of the upper lias and inferior oolite. 
These last mentioned divisions have also some 
Fig. 220. fossils in common, such as the 

Avicula itusquivalvis (Fig. 220.). 
Nevertheless the Lias may be 
traced throughout a great part 
of Europe as a separate and 
. independent group, of consider' 




th. XVIIL3 tiAS. 887 

able thiekness, varying from 500 to 1000 feet, 
containing many peculiar fossils, and having a 
very uniform lithological aspect. Although usu* 
ally conformable to the oolite, it is soilietimes, ad 
in the Jura, unconformable. Thus, in the en=- 
virons of Lons-le-Saulnier, for instance, the strata 
of lias are inclined at an angle of about 45^, while 
the incumbent oolitic marls are horizontal. 

The peculiar aspect which is most characteristic 
of the Lias in England, France, and Germany, i6 
an alternation of thin beds of limestone, with a 
light brown weathered surface, separated by dark- 
coloured narrow argillaceous partings, so that the 
quarries of this rock, at a distance, assume a striped^ 
and riband-like appearance.* 

Although the prevailing colour of the limestone 
of this formation is blue, yet some beds of the 
lower lias are of a yellowish white colour, and 
have been called white lias. In some parts of 
France, near the Vosges moxmtains, and in Lux- 
embourg, M. E. de Beaumont has shown that the 
lias containing GryphxBa arcuata^ Plagiostoma ffi- 
ganteum^ and other characteristic fossils, becomes 
arenaceous ; and around the Hartz, in Westphalia 
and Bavaria, the inferior parts of the lias are 
sandy, and sometimes afford a building stone 
called by the Germans quadersandstein. 

• Conyb. and Phil. p. 261, 
S 2 



lie name of Grypbite limestone has dometimt^ 
been ^plied to the lias, in consequence c^ the 
great number of shells which it contains of a 
species of oyster, orGryphsBa {Fig. 221.)' Matiy 
cephalopoda, also, such as Ammonite, Bd^nni^ 
and Nautilus (Fig. 222.), prove the marine origin 
of the ibnnation. 



Fig. 221. 



Ilg. a»i. 




The tbssil fish resemble generically those of the 
oolite, belonging all, according to M. Agassiz, to 
extinct genera, and differing remarkably from die 
ichthyolites of the cretaceous period. Among 
them is a species of Lepidotus {L.ffig<M, Ag.) (Fig. 
223.), .which is found in the lias of England, 



Fig. S89.' 




WHTHTOD0Bira.ITES. 



EnuHm, and Gtesmaay.* This genus was bdbre 
B^entioned (p. 346.) as occntriiig in the Wealdei^ 
and is supposed to have frequented both rivers 
and coasts. The teeth of a qtecies of Acrodus, 
also, are very abundant in the lias (Fig. 224.) 

Fig. 224. 




But the remmna of fish which have excited 
more attention than any others, are those large 
bony spines called ichthyodomlites (a. Fig. 225.), 




which were once supposed by some naturalists to 
be jaws, and by others weapons, resembling those 
of the living Balistes and Silurus; but which M. 
Agassiz has shown to be neither the one nor the 
other. The spines, in the genera last mentioned, 

* Agaani, Poii. Fos., vol. ii. td>. 2S, 89. 
B 3 



980 lCBTim>l>MUI>ITB& ptal IL 

ardoylate vidi the bockbooe, where&s tlm« are 
BO signs of any au^ articulation in the icbthyodo- 
ralitet. These last appear to have been bony 
spines which fonned the anteiior part of the 
dorsal fin, like that of the living genera Oeatracion 
and Chimfera (see a. Fig. 2^.)- ^^ both of these 

Fig. 326. K-y 



a. Spine fomisg aBtcnor patt of tbe donsl Sa. 
genera, the posterior concave face is armed with 
small spines like, that of the fossil Hybodus ( Fig. 
225.), one of the shark ^mily found fossil at 
Lyme Re^s. Such spines are simply imbedded 
ifi the flesh, and attached to strong muscke. 
" They serve," says Dr. Buckland, " as in the Chi- 
mera (Fig. 233.), to raise and depress the fin, 
their action resembling that of a moveable mast, 
raising and lowerii^ backwards the sail of a 
barge."f 

Reptiles of the Uas. — it is not, however, the 
fossil fish which ibrm the most striking feature in 

* Agaaui,PoiBsoiiH Fossilec TOLiii.t^C.figi 1. 
t Bridgewatw Timtiaa, f, 990. 



Ch, XVIII J BEFTILBS OF THE LIAS. 891 

the organic remains of the Lias ; but the reptiles, 
which are extraordinary for their number, size, 
and structm'e. Among the most singular of these 
are several species of Ichthyosaurus and Plesio- 
saurus* The genus Ichthyosaurus, or fish-lizard, 
is not confined to this formation, but has been 
found in strata as high as the chalk-marl and 
gault of England, and as low as the muschelkalk, 
a formation which immediately succeeds the lias 
in the descending order.* It is evident fi'om 
their fish-like vertebrae, their paddles, resembling 
those of a porpoise or whale, the length of their 
tail, and other parts of their structure, that the 
habits of the Ichthyosaurs were aquatic. Their 
jaws and teeth show that they were carnivorous ; 
and the half digested remains of fishes and rep- 
tiles, found within their skeletons, indicate the 
precise nature of their food.f Mr. Conybeare was 
enabled, in 1824, after examining many skeletons 
nearly perfect, to give an ideal restoration of the 
osteology of this genus, and of that of the Plesio- 
saurus.^ The latter animal had an extremely 
long neck and small head, with teeth like those 
of the crocodile, and paddles analogous to those 
of the Ichthyosaurus^ but larger. It is supposed 
to have lived in shallow seas and estuaries, and 

* Backlandy Bridgew. Treat., p. 168. 

t Ibid. p. 187. 

% Geol. Trans., Second Series, vol. L pi. 49. 

8 4 



I 






??. 



. -^. 



J^ 





^ 







to have breathed air like the lehthyosaur, and 
our modem cetacea.* Some of the repfCiles above 
mentioned were of formidable dimensions. One 
specimen of Ichthyosaurus phtyodan^ from the 
lias at Lyme, now in the British Museum, must 
have belonged to an animal more than twenty- 
four feet in length, and another of the l^l^iosau- 
rus, ia the same collection, is eleven feet long. 
The form 6f the Ichthyosaurus may have fitted it 
to cut through the waves like the porpoise ; but it 
is supposed that the Plesiosaurus, at least the long- 
necked species (Fig. 228.), was better suited to 
fish in shallow creeks and bays, defended from 
Heavy breakers. 

For the last twenty years, anatomists have 
agreed that these extinct saurians must have inha- 
bited the sea, although no living marine reptile 
was known. They argued diat, as there are 
now Chelonians, like the tortoise, living in fresh 
water, and others, as the turtle, frequenting the 
ocean, so diere may have been formerly some 
saurians proper to salt, others to freefk waiter. The 
recent discovery, however, of a maritiaie sauricm, 
has now rendered it unnecessary to speculate on 
such possibilities. This creatiure was found in the 
Galapagos islands, during the visit of H. M, S. 
Beagle to that archqpelago, in 18S5, and its habits 

* Conybeare and De la Beche» Oeol. Trans. ; and Buck- 
laad, Bridgew. Treat., p. 20a 

8 5 



were then Qbeetved^ by Mr. Darwijau The islands 
^lliided to are situated ugder the equator^ nearly 
60^ miles to the westward of the coast of South 
America. They are yolcanic, some of them 
being 3000 or 4000 feet high; and one of them^ 
Albemarle Island, 75 miles loi^. The climate 
is mild, very little rain &lls; ^d, in the whole 
archipelago, there is only one rill of fresh water 
that reaches the coast. The soil is for the most 
part dry and harsh, and the vegetation scanty. 
The birds, reptiles, plants, and insects are, 
with very few exceptions, of species found no- 
where else in the world, although all partake, 
in their general form, of an American cha- 
racter. Of the mammalia, says Mr. Darwin, 
one species alone appeajcs to be indigenous, 
namely, a large and peculiar kind of mouse ; but 
the number of lizaids, tortoises, and snakes is so 
great that it may be called a land of reptiles. 
The variety, indeed, of species is small ; but the 
individuals of each are in wonderful abundance. 
There is a turtle^ a large tortoise ( Testudo Indi- 
cus)^ four lizards, and- about the same number of 
s^akes, but no, frogs, or toadsu Two of the lizards 
belong to the, family Iffiumidm of Bell, and to 
a peculiar genus (AmblyrhyTichiLs) established by 
that naturalist; and so named from their obtusely 
truncated head and short snout* Of these li- 

* afi€Kvi:, amblysy blunt, and pvyxoff diynchus, soout. 



Ck-XTIIIO OF TUB OAIilfAeas ULAMD& 800 

vais, OBB is. tesreetzid ia its habitBi and barrem 
m the g^round, Bwannii^ eveiTrriiere oa the iaad, 
having a. round t^ and a.inoudi sMnewhat reaeofr 
bliniginibmLlhatofthetortoise. The other is aqua- 
tic, and has its tsJl SattaiedlaSeratiy for swinuning 
(see F^229.)- " This- marine saiuiian,'' says- Mr. 
Kg. stSi- 



Mt, BcU. Ltegtb mylng ftom 3 to t ft. 1%! aJu 
B. Tootli of same of natural aiie, and magnified. 

Darwin, " is extremely common on all the islands 
throughout the archipelago.^ It lives exclusively 
on the rock; aearbeaohes, and I never saw one 
even ten yards inshore. The usual length is 
about a yard, but there are some even four feet 
long. It is of a dirty black colour, sluggish in 
its movements, on the land ; but, when in the 
water, it swims wilJk piKfeot ease and quickness 1^ 
a serpentine movement of> itsr body and flattened 
tail, the legs during this, time being motionless, 
and closely collapsed on its sides. Their limbs 
and strong claws are admirably adapted for crawl- 
8 6 



^^^ jjn»o UAvaok fAuatAK. i ^&0tm 

kig o^rer the tugged and fiBSured maases <^ him 
which everywhere form the eoaat* . In sudi, ditun 
itiong 4 group of six or sev^^ of these hideow 
reptiles may oftentimes be seen on 4he Made 
rocks, a few feet above the sm^ baskiti^ in the 
sun with butstaietehed legs. Their stomabhsy eb 
being opened, were found to be largely distended 
with minoed sea-weed, of a kind which grows at 
the bottom of the sea, at some little distance firom 
the coast. To obtain this, the lizards are seen 
occasionally going out to sea in shoals* One of 
these animals was sunk in salt water, from the 
ship, with a heavy weight attached to it, and 
drawn up again after an hour; it was quite active 
and unharmed. It is not yet known by the inha- 
bitants where this animal lays its eggs; a singular 
&ct, considering its abundance, and that the 
natives are well acquainted with the eggs of the 
terrestrial AmblyrbynchuSi which last is also herbi* 
vorous, although feeding on a very di£b:«nt kind 
ofvegetaticMi.*** 

In those deposits now forming by the sediment 
waslied away from the wasting shores of the Gahr 
pages islands, the remains of sanrians, both of the 
land and sea, as well as of chelonians and fidii 
may be mingled with marine shells without any 
bones of land quadrupeds or batrachian reptiles; 

* Darwin's Journal, chi^. xix. (For full title, see note, 
p. 137.) 



d^. Vi^iL3 "tomius at IMS ttjii. $^* 

felts ei^n hei^e we should expeet the f^m^s:-d( 
marme mammalia to be imbedded in the neW 
strata, lor there are seals, besides several kinds 6f 
cetacea, on the Galopagian shores; and, in tfaid 
respect, the parallel between the modem IkxmBj 
above described, and the ancient one of the lias. 
Would not hold good. 

* Sudden de$tfuctUm ofsaurians^ 4*^. — ^It has been 
^marked, and tnily, that many of the fish and 
saunans, found fossil iii the lias, must have met 
with sudden death and immediate burial; and 
that the destructive operation, whatever may have 
been its nature, was often repeated. 

" Sometimes," says Dr. Backland, « scai^ely k 
single bone or scale has been removed from the 
place it occupied during life; which could not 
have happened had the uncovered bodies of these 
saurians been left, even for a few hours, exposed 
to putrefaction, and to the attacks of fishes and 
Other smaller animals at the bottom of the sea."* 
Not only are the skeletons of the Ichthyosaulri 
entire, but sometimes the contents of their stomachs 
still remain between their ribs, so that we can dis- 
cover the particular species of fish on which they 
lived, and the form of their excrements. Not un- 
firequentiy there are layers of these coprolites at 
li^fF^nt depths in the lias, at a distance fix>m any 
entire skeletons of the marine lizards fix)m which 

« Bridgew. Treat, p. 125. 



thiey ware demed». ^^ as if/' 8^ Mr.De la Becfae^ 
^< the muddy botUNoa of thts sea received small 
sadden acoemong. Qf matter firom. time to tigoB^. 
coTering up the ceproUtes and other exuviae 
which had accumulal^ during the intervals/'* 
It is furllier atat^ tbali) at Lyme Regis, thorn 
sur&ces only of the coprolites whidbi lay iq^r- 
most at thQ bottom oi the sea have suffered partial 
decay) fi;om the action of water before they were 
ooveied and protected by the muddy sediment 
that has afterwards permanently enveloped, them.f 

Numerous specimens of the p^x«and-ink. fish 
{Sepia loliffOy lin., Lolijfp vulgfiirvh Lam.) have 
also been met with in the lias at Lyme^ with the 
ink-bags sftiU dist^ndedi containing the ink in a 
dried stat^, chiefly composedi of carbon^ and but 
slightly impregOAted with carbonate of lime. 
These cephalopoda^ ih»refo^ must,, like the.aau- 
rianS) have, died 9uddenly9 and have been, in- 
stantly buried in sediment; fi)r, il exposed after 
death» the membmno: comaining the ink wwld 
have decayecL.}^ 

As we know tha^ river fish ue sometimes, 
sjtified^.even iatiteir own. element^ by muddy water 
during floods^it: caaxiot be dpubted that the pe- 
riodical discharge of lai^ bodies of turbid fii^esh 
water into the sea^ m^ be. still more fiital ta 

* Geological Researches, p. 334. 

f Buckland, Sri4gew..Treat,» ^.3197.^ t I^id. 



c^, vmti FOSSILS Of -vfis LUa- QM 

^arinQ tribea. hi the Priociplea of Geolog;, 1 
have sIfDwn how large quantitiea of mad and 
(Irowned animala are swept down into the sea by 
riven during earthquakes, as in Java, in 1699 ; 
and bow undescribabie multitudes of dead fish 
have been seen Hoating on the sea after a discharge 
of noxious vapours after similar conTulsions. * 
But, in the intervals between such catastrophes, 
strata maj^ have aecuijaulated eJowly in the sea of 
the liaa, some being formed chiefly of one descrip- 
tion of shell, sudi as ammonites, oUiers of gry- 
phites. 

^ouii planU. -r- Among the vegetable remuns 
of the Lias, several species of Zamia have been 
found at Lyme Regis,, and the remains of coni- 
ferous plants at Whitby. Fragments of wood are 
common, and often converted into argillaceous 
limestone. Tliat some of this wood, though now 
petrified, was soft when it first lay at the bottom 
Fig. sso. of the sea, is shown by 

E^tecim^i now in the 
museum of the Geological 
I Socie^ (see Fig. 230.), 
which has the form of an 
ammonite indented on its surface. 

Oriffin of the Oolite md lAat. — If we now en- 
deavour to restore, in imagination, the ancient 

* See Principles, Judex, Lancerote, OrahRiii Island, Co- 
■bm. 




4pp. oKionr of the cFtatn. 

oondition of the European area at the period of the 
Oolite and Lias, we must conceive a sea in whicli' 
the growth of coral reefs and shelly limestohesi^ 
after ' proceeding without interruption for* ages^ 
was liable to be stopped suddenly by the depo- 
sition of clayey sediment. Then, again, the ar-* 
gillaceous matter, devoid of corals, was deposited, 
for ages, and attained a thickness of hundreds of 
feet, until another period arrived when the same 
space was again occupied by calcareous sand, or 
solid rocks of shell and coral, to be again suc- 
ceeded by the recurrence of another period of 
argillaceous deposition. Mr. Conybeare has re- 
marked of the entire group of Oolite and Lias, 
that it consists of repeated alternations of clay, 
sandstone, and limestone, following each other in 
the same order. Thus the clays of the lias are 
followed by the sands of die inferior oolite, and 
these again by shelly and coralline limestone, 
(Bath oolite, &c.) ; so, in the middle oolite, the 
Oxford clay is followed by calcareous grit and 
** coral rag ;" lasdy, in the upper oolite the Kim- 
meridge clay is followed by the Wejrmouth sands 
and the Pordand limestone.* The day beds, 
however, as Mr. De la Beche remarks, can be 
followed over larger areas than the sands or sand- 
stones, f It should also be remembered^ that 

* Coo. and Phil. p. 166. f Geol. Researches, P 337. 



Gh.3CVliL3 OOLITE AND LIAS. 401 

wbil^ the oolitic system becoines arei\ac.eoiis, 9X^4^ 
resembles a coal-field in Yorkshire, it assumes, iii 
the Alps^ an almost purely calcareous form, the 
sancU and clayd being omitted; a:nd even. in the 
intervening tracts, it is more complicated and 
variable .than appears in ordinary descriptions* 
Nevertheless, some of the clays and intervening' 
limestones do, in reality, retain a pretty uniform 
character, for distances of from 400 to 600 mUes 
from east to west and north to south* 

According to M. Thirria, the entire oolitic 
group in the department of the Haute Saone, in 
France^ may be equal in thickness to that of Eng- 
land; but the importance of the argillaceous divi- 
sions is in the inverse ratio to tibat which they 
exhibit in England, where they are about equal 
to twice the thickness of the limestones, whereas, 
in the part of France alluded to, they reach only 
about a third of that thickness.* In the Jura the 
clays are still thinner ; and in the Alps they thin- 
out and almost vanish* 

In order to account for such a succession of 
events, we may imagine, first, the bed of the ocean 
to be the receptacle for ages of fine argillaceous 
sediment, brought by oceanic currents, which may 
have communicated with rivers, or with part of 
the sea near a wasting coast. This mud ceases, 

* Burat*B D'AubuissoD, tom.u. p. 456. 



408 KioiN or oouTs aiid uas. cv^n* 

at lengthy to be eoDY^ed to the smte region^ 
either because the land which had previously suf- 
fered denudation is depressed and submerged, or 
beeause the current is deflected in another direc- 
tion by the altered shape of the bed of the ocean 
and nd^ibouruig diry land. By such changes 
the i¥ater becomes (mee more clear and fit for the 
growth of stony zoophytes* Cakaieous sand is 
then formed from comminuted sheU and coral, or, 
in some cases, arenaceous matter replaees the 
clay, because it commonly happens that the finer 
sediment, being first drifted fiurtbest from coasts, 
is subsequently overspread by coarse sand, after 
the sea has grown shallower^ or when the land, 
increadipg in extent, has aj^roaehed nearer to the 
spots first occupied by fine mud. 

In order to aeeount for another great form- 
ation, like the Oxford clay, again covering one of 
coral limestone, we must suppose a sinking down 
like that which is now taking place in some exist- 
ing regions of coral between Aus^alia and South 
America.* The occsavven^e of wbridences, on so 
vast a scaler may again have caused the bed of the 
ocean and the a^joinii]^ land throughout the 
]Suropean area^ lo> assume a shape fim>urable to 
^ depositiqn eCanotter set of clayey strata; and 
thia change may have been suoeeeded by a series 

* See D9nm», chap, wk (fi>P ftill ti|l^ se» note, p. 187.) 



of events analogous to diat already explained, and 
these 9gain l>y a third series in similar order* 
Both the ascending and descending movements 
may have been extremely slow, like those now 
going on in the Pacific ; and the growth of every 
stratum of coral, a few feet in thickness, may have 
required centuries for its completion, during which 
certain species of organic beings may have dis- 
a^eared from the earth, and others have been 
introduced in their place ; so that, in each set of 
strata, from the Upper Oolite to the Lias, some 
peculiar and characteristic fossils were imbedded. 

Physical geography. — The alternation, on so 
larffe a scale, of distinct formations of clay and 
limltone, ba» given rise to some marked fiures 
in the [Epical outline of parts of England and 
France* Wide valleys can usually be traced 
throi^hout the long bands of country where the 
argillaceous strata crop^^ut; and between these 
valleys the limestones ave observed, composing 
ranges of hills> or more elevated grounds. These 
ranges terminate abruptly on the side on which 
the seyoral clays crop^ut from beaeath the cal- 
careous staratft. 

The annexed digram will give the reader an 
idea of the confignfatioa of tha sur&ee noir 
alluded ^> sudk as may be seen in passing from 
X^ondon to Cbeltenhais^ oc in odier paraUd^ Hues, 
from east to w^i, in the southern part of £i^«^ 




<4M VAttlSrs AKD ESCARPMSNTS' CPartll. 

Fig, SSi. 

laftrior lOUI* l^vir LMdon 

OgUM. Oolite. OoUte. ' Chalk, claj. 

liM. Osfoddv* Kim. day; Oaidt. 

landl It has been necessary, however, in this 
drawing, greatly to exaggerate the inclination of 
llae beds, and the height of the several formations, 
as compared to their horizontal extent. It will be 
remarked, that the lines of cliff, or escarpment, 
&oe towards the west in the great calcareous emi- 
nences formed by the Chalk and the Upper, 
Middle, aiid Lower Oolites ; and at the base of 
each we have respectively the Gault, Kimmeridge 
clay,' Oxford clay, and Lias. This last forms, 
generally, a broad vale at the foot of the escarp- 
ment of Inferior Oolite; but a considerable por- 
tion of that escarpment is sometimes occupied by 
lias* The external outline of the country which 
the geologist observes in travelling westward from 
Paris to Metz, is precisely analogous, and is 
caused by a similar succession of rocks inti^rvening 
between the tertiary strata and the Lias; with 
this difference, however, that the escarpments of 
Chalk, Upper, Middle, and Inferior Oolites, &ce 
towards the east instead of the west. 
. The Chalk cfopB*-out from beneath the terdary 
sands and clays of the Paris basin, near Epemay, 
and the Gault from beneath the Chalk and Upper 



to have breathed air like the Ichthyosaur, and 
our modem cetacea.* Some of the reptiles above 
mentioned were df formidable dimemions. One 
specimen of Ichthyosaurus platyodcm^ from the 
lias at Lyme, now in the British Museiimy must 
have belonged to an animal more than twenty- 
four feet in length, and another of the ?l6siosau- 
rus, in The same collection, is eleven feet long. 
The form of the Ichthyosaurus may have fitted it 
to cut through the waves like the porpoise ; but it 
is supposed that the Plesiosaurus, at least the long- 
necked species (Fig. 228.), was better suited to 
fish in shallow creeks and bays, defended from 
heavy breakers. 

For the last twenty years, anatomists have 
agreed that these ^tinct saurians must have inha- 
bited the sea, although no living marine reptile 
was known. They argued that, bh there are 
now Chelonians, like the tortoise, living in fresh 
water, and others, as the turtle, frequenting the 
ocean, so there may have been formerly some 
saurians proper to salt, others to frecfk water. The 
recent discovery, however, of a maritime saurian, 
has now rendered it unnecessary to speculate on 
such possibilities. This creature was fiamd in the 
Galapagos islands, during the visit oS H. M. S. 
Beagle to that archipelago, in 183^5, and its habits 

* Conybeare and De la Beche> Geol. Trans. ; and Buck- 
iaiidy Bridgew. Treat.^ p. 20a 

S 5 



were then obeecvecl by Mr. Darwip^ The islands 
plluded to are situated imder the eqiiaJtor^ nearly 
6Q0« miles to. the westward of the coasts of South 
America. They are volcanic, some of them 
being 3000 or 4000 feet high; and one of them, 
Albem^le Island, 75 miles loi^. The climate 
is mild, very little rain falls; and, in the wholje 
archipelago, there is only one rill of fresh water 
that reaches the coast. The soil is for the most 
part dry and harsh, and the vegetation scanty. 
Tl^e birds, reptiles, plants, apad insects are, 
with very few exceptipns, of species found no- 
where else in the world, although all partake, 
in their general form, of an American cha- 
racter. Of the mammalia, says Mr. Darwin, 
oi^e species alone appears to be indigenous, 
namely, a large and peculiar kind of mouse ; but 
the number of lizards^ tortoise^ and snakes is so 
great that it may be called a land of reptiles. 
The variety, indeed, of species is small ; but the 
individuals of each are in wonderful abundance. 
There is a turtle^ a large tortoise ( Testudo Indi- 
cus)i four lizards, and- about the same number of 
suakes, but no, frogs, or toads. Two of the lizards 
belong to the. family fyuanidce of Bell, and to 
a peculiar genus (AtnbfyrhyncAus) established by 
that naturalist; and so named from their obtusely 
truncated head and short snout.* Of these li- 

* afi€Kvc, amblys, blunt, andpvyxoff liiynchus, snout. 



latds, ooe is- tenrestrial ia its habite, and burrewB 
is the geeund, Bwarmii^ eveiTwhene on the land, 
baving a. round tail, andamouth SMnewhat reseok 
bliaginfiHrmthatofthetortoise. The other is aqu^ 
tic, and hafi its t^ flattened- laSeraJly for swinuning 
(see F^229.)- *' This-iaanne saunian," says Mr. 

Kg. 9E8;. 



JnHi/rliyiKAui criiianti, Bell. Ltngtb TUjittg ftam 3 to in. 7^ «% 

uMilw HwriH inarrf WB ihuaiM 

a. Tooth of suae of mtiinl aiie, and minified. 

Darwin, " is extremely common on all the islands 
throughout the archipelago.^ It lives exclusively 
on the rocky eearbeaohes, and I never saw one 
even ten yards inshore. The usual length is 
about a yard, but there are some even four feet 
long. It is of a dir^ black colour, sluggish in 
its movements, on the land ; but, when in the 
wato*, it swims with pcefeot ease and quickness by 
a serpentine movement of itSr body and flattened 
tail, the iegs. during this, time being motionlesa, 
and closely collapsed on its sides. Their limbs 
and strong claws are admiraUy adapted for crawl- 



^^ LHFINO MAHna 9AI»^AK. r'f^^^P^^ 

ii^ o^i^ear ihe tugged and Ba/iiareA maa$eBQ( laem 
which everywhere fi>nn the eoaat* t Insuchr^i^ 
itiong 4 group of six or seven of these hideow^ 
reptiles may oftentimes be seen on 4he Ueck 
rocks, a few feet above the sui^ baskii^ in the 
sun with butstietehed legs. Then: stomachs, ob 
being opened, were found to be largdiy dist^dad 
with minced sea-weed, of a kind which grows at 
the bottom of the sea, at some little distance firom 
the coast. To obtain this, the lizards are seen 
occasionally going out to sea in shoals. One of 
these animals was sunk in salt water, from thia 
ship, with a heavy weight attached to it, and 
drawn up again after an hour ; it was quite active 
and unharmed. It is not yet known by the inha* 
bitants where this animal lays its eggs; a singular 
fact, considering its abundance, and that the 
natives are well acquainted with the eggs of the 
terrestrial Amblyrh^nchtu, which last is also herbi« 
vorous, although feeding on a very diffi»:«nt kind 
of vegetation.*** 

In those deposits now forming by the sediment 
woEJied away from the wasting shores of the Galar 
pagos islands, the remains of sanrians, both of the 
land and sea, as well as of cheloniims and fish^ 
may be mingled with marine shells widiout any 
bones of land quadrupeds or batrachian reptiles ; 

♦ Darwin's Journal, chap. idx. (For full title, see note, 
p. 137.) 



y«f eWn hei*e we should expect the i^rtiaifis;^ 
marme mammalia to be imbedded in the neW 
sirata, lor diere are deals, besides s^?ieral kindsr 6f 
cetacea, cm the Galopagion shores; cmd, in ttdd 
respect, the parallel between the modern fii,una, 
ihove described, and the imcient one of the liais, 
wotdd not hold good. 

* Sudden destruction ofsanrianSi 4^e. — « It has beeh 
remarked, and truly, that many of the fish and 
saurians, found fossil in the lias, must have met 
with sudden death and immediate burial; and 
that the destructive operation, whatever may have 
been its nature, was often repeated* 

" Sometimes,'* says Dr. Buckland, ** scarcely k 
single bone or scale has been removed froni th6 
place it occupied during life; which could not 
have happened had the uncovered bodies of these 
saurians been left, even for a few hours, exposed 
to putrefaction, and to the attacks of fishes and 
Other smaller animals at the bottom of the sea.''* 
Not only are the skeletons of the Ichthyosauri 
entire^ but sometimes the contents of their stomachs 
still remain between their ribs, so that we can dis- 
ooter the particular species of fish on which they 
lived, and the form of their excrements. Not un- 
frequentfy there are layers of these coprolites at 
difE^nt depths in the lias, at a distance firom any 
entire skeletons of the marine lizards from which 

« 

* Bridgew. Treat, p. 125. 



9^ LIYOiO 1CA»I» 9AOBIAK. r . ^^f^ Jld 

is^ 0\i€Br the rugged and fisiured meaaeB 4i£ lavft 
which eveipywhere £>rin the eoaat* « Insuch^iii^iin 
itiong 4 group of six or seven of these hideoms: 
reptiles may oftentimes be seen on cbe black 
rooks, a few feet above the sui^ baskiii^ in the 
sun with butstietehed legs. Their stomabhsy ob 
being opened, were found to be largdy diat^dad 
with minced sea-weed, of a kind which grows at 
the bottom of the sea, at some little distance from 
the coast. To obtain this, the lizards are seen 
occasionally going out to sea in shoals. One of 
these animals was sunk in salt water, from thia 
ship, with a heavy weight attached to it, and 
drawn up again after an hour; it was quite active 
and unharmed. It is not yet known by the inha* 
bitants where this animal lays its ^gs; a singular 
fiict, considering its abundance, and that the 
natives are well acquainted with the eggs of the 
terrestrial AmblyrhffnchtUj which last is also herbi- 
vorous, although feeding on a very di£^:^nt kind 
of vegetation.** * 

In those deposits now forming by the sediment 
washed away from the wasting shores of the Galar 
pagos islands, the remains of saurians, both of the 
land and sea, as well as of chelonians aad fish^ 
may be mingled with marine shells without any 
bones of land quadrupeds or batrachian reptiles ; 

♦ Darwin's Journal, chap. xix. (For full title, see note, 
p. 137.) 



fm eWn hefe we should expect the iteitiaiiis; df 
marme mammalia to be imbedded in the'neW 
smita, lor ^ere aife deals, besides s^?ieral kindsr 6f 
o^tabea, cm the Galopagian shores; and, in ttdd 
respect, the parallel between the modern faunie^ 
ihove described, and the imcient one of the lias, 
#o«dd not hold good. 

* Sudden dettruction ofsaurums^ 4^e. --« It has beeh 
remarked, and truly, that many of the fish and 
saurians, found fossil in the lias, must have met 
with sudden death and immediate burial; and 
tliat the destructiye operation, whatever may have 
been its nature, was often repeated. 

^^ Sometimes,'' says Dr. Buekland, ^ scarcely k 
single bone or scale has been removed from th6 
place it occupied during life; which could not 
have happened had the uncovered bodies of these 
saurians been left, even for a few hours, exposed 
to putrefaction, and to the attacks of fishes aiid 
Other smaller animals at the bottom of the sea." * 
Not only are the skeletons of the Ichthyosauri 
entire^ but sometimes the contents of their stomachs 
still remain between their ribs, so that we can dis- 
ooter the particular species of fish on which they 
lived, and the form of their excrements. Not un- 
frequentfy there are layers of these coprolites at 
dtiffi^nt depths in the lias, at a distance firom any 
entire skeletons of the marine lizards firom which 

* Bridgew. Treat, p. 125. 




rosaii. rooTTTEPs. [notu. 

For this unknown aoimal 
Professor Kaup has proposed 
the provisional name of Chi- 
rotherium; and he conjectures 
that it ^vaa a mammiferoos 
quadruped, allied to the inar- 
supialia.* 

In the kangaroo, says Dr. 



Fig. 239. 

^<fe ^*;^ ^^, 

XiJM iiffooltteft Oft tiab iff tandttoiu. BUdAurg^mtien, iW Saam^. 

fore-foot is, in a similar manner, set obliquely 
to the others, like a thumb; and the dispro- 
portion between the fore and hind-feet is also 
very great. If it should be eventually proved 
that this animal was really marsupial, these fossil 
relics belong to the most ancient mammiferous 
quadruped yet known to palaeontologists. 

It would scarcely be possible to draw a distinct 
line of demarcation between the Keuper and 
Bunter Sandstein, in Germany, where they are 
not barren of fossils, if the Muschelkalk did not 
intervene between them. In England, therefore, 
where this calcareous formation is wanting, and 
where there are scarcely any organic remains in 

* See Buckland's Bridgew., p. 263. 



■ « t 



Ch.XIX.3 LOWER NEW RED SANDSTONE. 413 

the Upper New Red marl and sandstone, we can* 
jnat feel assured that the divisions cu and 'c. of oiir 
Table^ p. 407., do really coincide with the Ger* 
man Keuper and Bunter Sandstein* But it has 
been found convenient in the counties of Salop^ 
:StafFord9^nd Worcester, to divide the saliferous 
inarls from the inferior quartzose conglomerate in 
the manner above indicated. 

LOWER KEW RED SANDSTONE AND MAGNESIAN 

LIAfESTONE. 

• # - 

We now come to the Lower New Red system, 
the position df which can best be determined in 
Germany, because it is there interposed betweeil 
the Coal and Bunter Sandstein, or oldest part of 
the " Upper New Red,*' above described. In the 
south-west of England the New Red sandstone 
formation is unconformable to the Coal (see Fig. 
232.) ; but in the north-east of England Professor 
Sedgwick has shown that the same series is con- 
formable to the carboniferous strata, and passes 
into them. In other words, the movements which 
deranged " the Coal'* in tfie south-west, pre- 
viously to the origin of the New Red sandstone, 
did not extend towards Durham and the more 
northern counties. 

Near Bristol, in Somersetshire, and in other 
counties bordering the Severn, the unconformable 
beds of the Lower New Red, resting immediately 

T 8 



414 UOWEK HEW BED (Tirta 

upon tHe Coal, consist of a cmiglomerate caUei 
<< dblomidc,'' because the pebbles of older rodcs 
are cemented togedier by a basQ of magnesian 
limestone. Among the imbedded pebbles are 
many derived from the Cool, particularly from 
the carboniferous limestone^ the peculiar fossils of 
which are still seen in many large rounded frag- 
ments. In the north-east of England the dolomitic 
conglomerate is represented by a yellow lime- 
stone, generally called the Magnesian Limeston^ 
which passes upwards into marl slate, and down- 
wards into red marl and gypsum* In the inter- 
mediate counties of Worcestershire, Staffordshire^ 
and Shropshire, arie conglomerates referred to the 
same age, but which are calcareouB, with scarcdty 
any magnesia. Between these conglomerates and 
the Coal is a great formation, called the Lowar 
New Red sandstone (see Table, p. 4(>7.)9 com- 
posed of sandstones, red shales, and marls, occa- 
sionally spotted green.* 

The country of Mansfeld, in Thuiingia, may 
be called the classic ground of the Lower New 
Red, or Magnesian Limestone formation, on the 
continent. It has there been long cdiebrated^ be* 
cause one of its members, a slaty marlstone^ h 
richly impregnated with copper pyrites^ for which 
it is extenjuvely worked. The formatbn in that 

* MurcbisoD^ Sfluriaii System,, p. S4. 



CkXtX.] AND MAOKESIAK LIMESTONR 415 

eonntry k composed of an upper calcareous divi- 
sion, called the Zechstein, and a lower red quart> 
zose formation pf sandstone and conglomerate^ 
called the Rothliegendes* The upper of these 
systems is very complex, consisting of marl, lime- 
stone, copper-slate, magnesian limestone, gypsum, 
and rock-salt, in which numerous fossils occur, 
bearing a striking generic resemblance to those of 
oiur English Magnesian Limestone. The Lower 
system, or Bothliegendes, is interposed between 
the Zechstein and the Coal ; and is supposed to 
correspond with the Lower New Red sandstone, 
above mentioned, as occupying a similar place in 
England between our Magnesian Limestone and 
Coal* Its local name of Bothliegendes, redrlyerj 
or " Roth-todt-liegendes," redrdead-lyer^ was given 
by the workmen in the German mines from its 
red colour, and because the copper has died out 
when they reach this rock, which is not metalli- 
ferous. It is, in fact, a great deposit of red sand- 
stone and conglomerate, with associated porphyry, 
basaltic trap, and amygdaloid. 

When we consider the fossils of the Magnesian 
Limestone in England, or corresponding Zech- 
stein in Germany, we find that they approach 
much nearer in their character to the organic 
remains of the older carboniferous group than to 
those of the Upper Kew Red. Thus, for example^ 
the two geneva of shells, Prodlieta ftnd Spirifer, 

T 4 



lii 



Fossius or 



ti^ii 



of >die femily Brachiopoda, are commofi td the 
Magnesian Limestone, Coal, and Primary fbssQi- 

* • 

Rg. 240. Fig. 241. 





Produda calva. Sow. 

{Lepieend, Dalnuui.) 

MagDOuan limestoDe. 



Sjririfar mmtbiMm, Sow. 
Mafnerian Ximestona 



ferous Strata, but have never been met with in 
any rock above the Magnesian Limestone. T^ere 
are certain fish also found both in England and 
Germany? lA the Lo^er New Red system, which 
occur in the carboniferous strata, but in no fonn- 
ation higher in th^ series than the Magnesian 
limestone, not even }n the Musch^lk^lk. 

Fig. 243, 




Restored omtUne qf ajUk of ike genu^ Pai^<mi$cu9. Agaif. * 
Magnaiian limestone. 

The genus Palceoniseusj Agas. (Palao&rissym^ 
Blain.) is the most striking example, as t}iree 
species have been found in Englapd in ^larl jslate, 
immediately below the Magnesiai} LJmestone; 



* Poissons Fossilesy voL i. tab. A. fig. f , 



Q^.4^G^] THE HAC^pSI^^ .X^MESTONE. ^||^' 

1^14 fifr^ othi^r dlflferent^ >iit Jomrly allied spe^ 
cies, ill the ^te of the Zechstein of Gepnany,* ' 

It was first pointed out by M • Agassiz, that 
all the bony fish of the Magne^ian Limestone^ 
and qS t£B. the more ancient formations, have the 
vertebral column contmued into the upper lobe 
of the tail^ wkich is much longer than the lower 
lobe (see Fig, 242.), whereas, in strata newer 
than the Magnesian Limestone, the tail-fin is di- 
vided into two equal lobes, as in almost all living 
fishes, the vertebrae not being prolonged into 
either lobe. 

The remains of at least two saurian animals pf 
new genera, Palsbosaurus and Thecodontosaurus 
have been lately discovered in the dolomitic con* 
glomerate near Bristol, f They are allied to the 
Iguana and Monitor, and lore the most ancient 
examples of fossil reptiles yet found in Great 
Britain. The Zechstein of Germany is also th0 
oldest rock on the continent in which Saurian 
remains have been ibund« They are referred to a 
genus called Protorosaurus, also allied to the 
Monitor* 

The resemblance above alluded to between the 
fioissib of the Lower New Red system and those of 
Ae Coal^ ia not confined to the moUusda, fish, dnd 

* Sedgwick, Gteol. Trans., Second Series^ voLiii. p. 117. 
f. See pf^r by Messrs. Riley and Stuchbury^ Proceedings 
Geol. Soc. No. 45. 

T 5 




l>t» ««• r^iWa, bat attnda to the Crinoi- 
1, or &Da»>Ulica. Tlias me 
apeeiM^ die G/a&oeriaiteM pUams 
(Fig. iU&) of the MigtuwsD 
Limntooe of DwliaBi, has been 
id»tified by Mr. Miller witk a 
foasil of tbe Moiintun limcBtooe of 
KrktoL* 

Origin of ike New Ad Sm^Mtame 

.jmm, group. — The red ntidBtone and 

ioSIIjSmw. red Bawl, irttidi, in point of Atek- 
nesB, form the most considerable part both ^the 
upper and lowo' Keir Red fimnaUoa in England 
and Germany, any laro ariioi in great part from 
^Ak diunt^radrai of various cryBtalliD^ or meta- 
morphic schists; and somettmea, as in parts (tf 
8ax<my and Deron^ure, from porpbyritic tz^ 
foeks contaming macb oxide of iron. Id some 
diBtriot* of Ae eastern Ors^iaas in Scotland, as 
in tbe ncMth of Forftrshire, the sides of mouDtame 
composed of gn^sa, mica^chist, and day-dbtc^ 
are covered with alluvinm, derived from the di»- 
integradon of those rocks; and the mass of de- 
tritus is stuned by oxide of iro^ of precisely the 
same ctdour as the OHd Red sandstone t£ tbe 
adjoining Lowland*. Now tbis aUnvima merely 
requires to be swept down to the sea, or into a 

* Sedgwick, GeoL Tnuu., Second Serie*, toL i2. p. IM. 



Ob. XIX.] RED SAHBBTOm AND MARL. 419 

hke^ to form strata of red sandstone and red 
marl, similar to those of the ^^ Old Red" or New 
Red system, or those of the cretaceous era .in 
Spain (see p. 343.)9 oi* tboge of tertiary origin, as 
at Coudes and Champheix, in Auvergne, all of 
which are in lithologlcal characters quite undis- 
tinguishable from one another. The pebbles of 
gneiss in the tertiary red sandstone of Auvargne, 
point dearly to the rocks from which it has been 
derived. The red colouring matter may have 
been furnished by the decomposition of horn- 
blende, or mica, which contain oxide of iron in 
large quantity (see p. 167*). 

It is a general fact, and one not yet accounted 
for, that scarcely any fossil remains are preserved 
in stmtified rocks in which this oxide of itoA 
abotmds; and when we find fossils lA the New or 
Old Red sandstone in England, it is in ^ grey, 
and usually calcareous beds^ that they occinr. 



T 6 



J ?,* -•• ■-. 4m 



• ' ' «. 



' /. 



» 

1. • 



CHAPTER XX- 

THB COALy 09, CAR^QNIFERQU? 6B0UP, 

Carboniferons strata in the south-west of England — Saper- 
position of Coal-measures to Mountam limestone — De- 
parture from this type in north of England and Scotland — 
Freshwater strata -r- Intermixture ^f freshwater and marine 
beds -^Sauroidal fish — Fossil plants — Ferns and Sigil- 

' lariae — Lepidodendra — Calamites — Coniferse — Stig- 
manas. 

The next group which we meet with in the de- 
pending order is the Carboniferous, commonly 
palled " The Coal," because many beds of that 
mii^ersJ, in ^ more or less pure state, are inter- 
stratified with sandstone, shale, and limestone^ of 
which t^be buU^ pf the formation uk made up. The 
combustible coal itself, even in Great Britain and 
Belgimn, where it is most abundant, constitutes 
but a small proportion of the whole mass. In the 
north of England, for example, the thickness of 
the coal-bearing strata has been estimated at 3000 
jfeet, while the various coal*seams, 20 or 30 in 
number, do not exceed 60 feet.* 

In the south-west of England, in Somerset* 

* Fbillips ; art. ** Geology," Encyc. Britan. 



Ch. XXJ CARBONIFSBiliJS GROUP. 421 

shire, and in South Wales, the Carboniferous 
seriei^ consists of, 

r Strata of shale, sandstone, and grit, wit|| 
1st Coal-measures. •{ occasional seams of coal, sometimes ex- 

L ceeding 600 feet |q thickness, 

1A coarse i^uartiose sandstone passing into a 
conglomerate, sometimes used for mill« 
«ton£s; devoid pf coal; occasionally aboyo 
600 fe^ thick. 
3d. Mountain or f A calcareous rock containing marine s}iellB 
Carboniferous -I and corals, devoid of coal; thickness 
. limestone. i variable; sometimes 900 feet. 

Beneath all these is the Old Jled sandstone, 
which was formerly considered as part of thfj 
Carboniferpus series ; but which, now that its 
organic remains are better kn^wn, appears entitled 
to rank as a distinct formation. . 

Aswe proceed northwards from South Wales 9^d 
Somersetshire tg Yorkshire and the more north^nx 
counties, we find the Carboniferous group beginr. 
ning gradually tq assume a new character, ther^ 
^ing first a slight intermixture of the Cq^ 
me^ures and Mountain limestone at their conr: 
tact, and these alternations taking pl^oe afterward^ 
on a» ^till greater scale. The Coal, in Yoir]i;shire^ 
does not crease when we reach the MillstoipLi^grit]( 
although it is there in diminished quantity ; and 
b^aieiLlb that grit is a complex deposit 1000 feet 
thick, of limestones, alternating with coal-bearing 
sandstones and shale, bel6w which comes the great 



of moiititaiii limestone* In Bootknd vft 
obBerve a still wider departure fitm liie type ^ 
the south of England, the mixture of marine 
limestone with sandstone and shale, containing 
coal being mmr^ eompkite. 

Ilie importance of th^ coal In England, ecm- 
sidered economically, is greatly enhanced by the 
rich beds of iron-ore which occur in the associated 
shales, and the contiguity of the mountain lime- 
stone which is reqmred as a AvoL to reikice the 
iron-ore to a metallic state, f 

It is now generafiy admitted, that all coal 10 of 
vegetable origin, the vegetable stiticttire being 
still recognizable in many lands of coal, when 
slices thin enough to ttansmtt fight ore obtained 
and examined by the microscope. Impressions 
also of plants, together with entire tmnks of trees, 
are frequently met with in the accompanying 
shale and sancbtone; lesLVei also, and smafl bran« 
ches, and fruits, occur in nodnles of clay-ironstone^ 
the inclosed vegetable having served as a nudeus 
round which the ferruginous matter, usually caN 
bonate of iron, has concreted* Some of the coat" 
measures are of freshwater origin, and may have 
been formed in hkes^ othersseem to have been de^ 

« 9edginck; GeeL Tma^ Secoad ftiies, ftil.iirv; and 
PhiUiiNi,OeoLof Y4>rk8l^ part 9r 
f Conybeare, OuUinea^ &c., p. 333. 



posited ID eBtuilrie^ or Bt the mooths of riveia^ in 
Bpaeea alternately occupied byftceb and salt voter. 
Tliiis a freflhwater de|)08it, near Shrewsbury^) bas 
been ascertained by Mr, Murebiaon to be tbs 
ytningeat member of tho earboniferooB series of 
that district^ at the ptHnt where the coal-^neasBres 
pass into the lower New Red formation. It consists 
of shales and sandstones about 150 feet thick, widi 
coal, and traees of pkuts, including a bed of 
limestone, varying from two to nine feet la 
thiekness, which is cellular, and resembla the 
lacustrine limesttme of France and Germany. It 
has been traced for 80 miles in a straight Hne^ and 
recognized at more distant points. The chaiao- 
teristic fossils are a nnall bivaWe, having the fbim 
of a cydas, a small c^^iHis, (Fig. 245.) and a 
mierose<^c shell, (microctmchus) <^ an extinct 
genus. 

Elg. 344. Fig. 945. ' 




424. JP0891LS o; th« irwtiL 

. Bmt in the lower -eoal^measure^ of Q^albrook; 
Dale^ the Btxata, according ip Mr. Prest^yich, often, 
change completely within vepy ghort distances,, 
beds of sandstone passing horizontally into claj^ 
and day into sandstone. The coal*seams often, 
wedge out or disappear; and sections, at places 
tiearly contiguous, fNresent marked lithological 
distinctions. In this single field, in which the 
strata are from 700 to 800 feet thick, between 
40 and 50 species of terrestrial plants have been 
discoTeredy besides ^veral fishes a^d trilobites; 
the latter distinct in form fi:om those Qccarring 
in the Silurian strata. Also upwards of 40 specie$ 
of moUusca, among which are two or three pf th^ 
fireshwater geniis Unio, and others of marine forms 
such a^ Nautilus, Orthoceras, Spirifer, and 
Productus. Mr. Prestwicb su^ests, that the inter* 
mixture of beds containing freshwater shelly with 
others fiiU of miarine remains, and the alternation 
of coarse sandstone and conglomerate with beds 
of fine clay or shale containing the remains of 
plants, may be explained by supposing that the 
deposit of Coalbrook Dale, originated in a bay of 
the sea or estuary into which flowed a considerable 
river subject to occasional freshes.* 

In the Edinburgh coal-field at Burdiehouse, 
fossil fishes, mollusca and cypris, very similar to 

♦ Prestwich, GeoL Soc. Proceedings, No. 46. Murchison, 
Silurian System, p. 105. 



[LXX.} CARBONIFBHOUS QBOtTT. 40^' 

t&oae in Shropshire and Staffordshire, have been 
found by Dr. Hibbert.* In the coal-fietd also of 
Xorkshire there are freshwater strata, some of 
^ich contain shells referred to the genus Unio ; 
but in the midst of the series there is one diio but 
very widely spread stratum, abounding in marine 
shelly such as Ammonites Lideri (Fig. 246.) Or- 
tkoceras, Pei^en papj/raceia (Fig. 247.), and several 
fishes, f 

Rg. S46. Tig. 847. 





Pulta fofiiraettiM, Sow. 

^0 similarly intercalated layer of marine shells 
has been noticed in the neighbouring coal-field of 
Newcastle, where, as in South Wales, and Somer* 
setshire, the marine deposits are entirely below 
those containing terrestrial and fi-esh-wat^ 
remains.^ 

No bones of mammalia or reptiles have as yet 
been discovered in strata of the carboniferous 
group. The fish ^re numerous, and for the most 
part very remote in tlieir organization &om those 

* Trans, R07. Soc Bdin. toI-xui. Horner, Edin. New 
Phil. Jmim., April, ie.%. 
t Phillips; art, " Geology," Encyc Metrop., p. 590. 
X Hud., p. 592. 



IOC FosRO. nsH or tbk coal. tfunn. 

now lirin^, as tbey bdofig chie% b> &e Sadnrid 
fiuufy of Agassiz; u M^aficfadiys^ Holoptj"* 
efaiu, and others, «^ich were t^^ of great site^ 
and all predaoeoat. Their Mteology, says M. 
AgaBBU, reminds iu in many respects of the skd^- 
^ Fig. mi. tons of saurian reptiles, both 
by the dose satures ot the 
bones of the akuli, their larg« 
conical teeth striated longittN 
duially (see Fig. 24a), the ai^ 
ticulations of the spinous pro- 
cesses with the vertebrae, and 
other characters. Yet they do 
not form a femily intermediate 
between fish and reptiles, but 
^^^^ . are truejSsft.* 

^"■^^^Sf '^^ annexed figure repre- 

sents a large tooth of the Megalichdiys, found by 
Mr. Homer in the Cannel coal of Fifeshire. It 
probably inhabited an estuaiy, frequenting both 
the mouths of rivers and the sea. 

Fossil Plants of the Coal — But the flora of the 
coal forms the most interesting feature In its pa- 
leontology, and is fer better known to us than 
any other flora antecedent to the tertiary era. 
About 300 species of terrestrial plants are enti- 
merated by M. Adolpbe Brongniart ad prc^a^ to 

• AgasoE, PoiBS. Foss^ lirr. 4. p. BZ. aiid livr. S. p. 66. 




Gk.JUC.3 FOSSIL <70AL^I»J.KTS. 427 

tbe Coal» but botanists haye enoomitered Hm 
greatest dijBGicuIty in determining the natural sJBh 
nities of these fossils, it being rare to find in 
them any vestige of flower, seed, or fruit, those 
organs which afford the most convenient cha- 
racters for classifying living plants. They have 
been obliged, therefore^ first to study more mi- 
nutely the different forms of bark in existing 
trees, their various modes of branching, the tissue 
of their wood, nervures of the leaves, and other 
peculiarities of vegetable structure which might 
enable them to institute a direct comparison be- 
tween the analogous parts of recent and fossil 
plants,* 

The most common of these vegetable remains 
may be provisionally classed under the following 
heads: — First, Ferns and Sigillariae; secondly, 
Lepidodendra, allied to Lycopodiacece? thirdly. 
Catamites, allied to JSquisetacetB ? fourthly. Coni- 
ferous plants; fifthly, Stigmarise, apparendy an 
«tinct family of plants. 

Ferm and SigiUaruB* — The leaves, or more pro- 
perly speaking the fronds, of fernj» (see Figs* 249,^ 
250.), for the most part destitute of fructification, 
eJ&ceed in number all other plants in the shale of 
the coaL They have been divided by M. Ad. 
Brot^gniart into genera, characterized chiefly by 
the branching of the fronds, and the way in which 

* See the works of MM. Ad. Brongniart, Sternberg, and 
otiiersi and Ike Fossfl Flora of Lndley and Htitton. 



iSS tOSSIL W.AMT8 tP«lIt 

As veins of the leaves are disposed. "Hiese fronds 
are often accompanied by large fluted sterna or 
- FEg. E4». FSg. 350. ' 




PetafterUlamMtlea. 0. MUatpliTU er. 

(Fmi. Fla U3.) A. The uine, miadBed. 

[FOk Ilo. 101} 

tninks of trees which have been squeezed down 
and flattened as they lay prostrate in the shale, 
BO that the opposite sides meet, hut which when 
they occur in the accompanying grit or sandstone, 
and are placed obliquely or Tertically to the planes 
of stratification, are round and uncompressed. 
Their bark has been converted into coal; and 
diey must have been hollow when first deposited, 
for the interior became filled, not only with sand, 
but vith leaves and branches of ferns, introduced 
from above, Impressums of these fronda are. 



Ch. XX.] OF THE COAL-TTBATA, 4$t9 

i^w ^^uetft in the pillars of sandstone, wbii^ 
may be regarded as casta of the interior of thifs^ 
ancient trees> Most of the trunks of atcn^ now 
alluded to have.been called SigiUariffi. ,The; vat^ 
from ItalfA fi>ot to five feet in diameter, and must 
have been sometimes forty or fi% feet high. 

It is admitted by all botanists that some of these 
gi^antio stem^ all <^ which are comprehended by 
Brongniart in his genus Sigillaria, were true ar- 
borescent ferzis, as for example, that section which 
has been named Caulopteris by Lindley and 
Hutton. (see Fig. 251.) But these are compara- 
tively rare, whereas of the oilier section (Fig. 



r>g. 231. 



Kg. 252. 




Sigillaria Itilgala, Btoag. 



StiMarla LinUr^. Bnmi. 

252.) more than fort? species have been described. 
Id these ^e scars on the stem are smaller and 



more r^aWlj arranged in parallel series on Ae 
finted bark (Fig. SS2.) 

The recent tree-femff bdong to one tribe (iV 
^podiacea),tatd to asmall mnnber only of genera 
in diat tribes in all of irhich Ae sarfiice of die 
trunk ifl marked with scars, or eicatriceB, 1^ t^Rer 
Ae &11 of the frwids. Tliefie aeus axe preeat^ 
nmilar to those of Caul<^teriB (f^. SSI.); bat 
Mr. Lindie^ objects to the t^imoB that the re- 
maning Sif^llaris of Brongniart v^re Tree^^n^ 




Fig. 953. Fig. SJ4. Fig. 355. . 

Fig. 2S3. Tree fern from Iile of Bourbon. 
I^ 854. (^kea gbmea, Haoritiiia. 
Fig. 355. Tree fern from Braiil, 

because the scars in these are smaller, dissimilar 
in form, and more regularly arranged ifi parallel 



Ck.KX.] FOSaiL OeuL.H.AHTEL 4^ 

lines; also, because ibe stems are fluted (gee 
Fig. 252.), and BometimeB bifuresting. M.Bf<wgi., 
quTt hn tepilie^ that the forking of tbe steuti (^ 
aoiae of the &asil trees is no mere thaa mi^t 
haite been expected &<hd dieir h^ge aiie; and as 
to die fwms of the discs or scan from which the 
fconda have fidlm* their indindiwl variations aw 
B0t grceto' thaa those which we find in the fronds 
of different genera of living fema, which do net 
in the preeem (tale of the globe attain the size of 
txees. 

LepidodenA'a. — ■ Another class rf" fi^eaUs, very 
oenunoti in the eotU-shales, have been named Le< 
pidodendra. Some of these are of small size, and 




Tig. 95S. 

Mewcutle. ' 

Fig. 25S. Branching iniak, 49 feet long, inppowd to bare be- 
longed to L. SlentbergiL (Fos& Flo. 303.) 
Fig. S5T. Brandnng Men wMi buk and kaies of L. aunttergiL 

(Fon. Flo. 4.) 
Fig. 35S. Fonion of lama oanr the root; natural site. (IbiiiJ 



voanL n-AJOi > 



[IW» 



^fKroach very p«ar in . forin to dvt. a^^astx fstj- 
podiimu, or . clulwaosses, ^hile otbecs „of iimk^ 
lai^r dimensions are snf^Koed to h^ve been,!^ 
termediate between these andconij^QiK'plFiptli 
The annexed figures represents large fiisnlr i-fif/r 
dodendron, Ibr^-nine feet long^ Utdy "foupl is 
Jaerow CcJlieiy^ near Newcagjd^ lying in s^ate 
parallel to the planes of stratificatiOD. Fragpn»|y 
of others, found in die same shale, in^licate by th« 
eize of the rhomboidal scars which coves' them a 
still greater magnitude. The living club-mosses, 
of which there are about 200 q>ecies, are abundant 
in tr^tcal climates, where one species is sometimes 
met with attaining a height of three feet. They 
uBuallj creep on the ground, but some stand erect, 
as the Z. denaum, &om New Zealand (Fig. 259.). 



Kg. 259. 




Calamitea, — These fossils have a jointed stem 
longitudinally striated, and are supposed by M. 
Brongniart to have been allisd to the EquisetacetB, 



OF TBE COAL SIEATA. 



w Vfrac ^a^ tribe ; aqaatic [dants wliich, in a livii^' 
atftt^ arc only two 6t three feet high ' in our cli- 
Bntes, and even in tropical countries only attain, 
n in the case of Equwhtm giganteum, discovered 
by Humboldtand Bonpland, in South America, a 
height of about five feet, the stem being an' inch 
ID diuneter. The Calamites, however, of the Coa! 
di^red from these, principally in being furnished 
with a thin bark, which is represented in the stem 
of C. Suckowii (Fig. 261.), in which it will be seen. 



Fig. sei. 




that the Btriped external pattern does not agree 
with that left on the stone where the bark ia 
stripped off, so that if the two impressitms were 
seen separately, they might be mistaken for two 
distinct species. 

Ctmifera. — The structure of the wood of cer- 
t^n coal plants displays so great an analogy to 
that of certain pines of the genus Araucaria, as to 



lead to the opinion that some species of fira 
ecisted at this period. (See above, p. 8Q.) 

Stigtnaria. — Fragments of a plant which has 
been called Stigraariajicoidea occur in great num- 
bers in almost eveiy coal-pit. It is supposed to 
have been a huge succulent water-plant of an ex- 
tinct family ; thin transparent sections of the stem 
exhibiting an anatomical structure quite different 
from the wood of any living tree,* According to 
Fig. 362. 




Smfaet iffaroltir iHtMiHl qf 



Fig. 263, j[jg conjectures of some bot- 

anists, it approached most 
nearly to the family Lycopo- 
diaeecB ; according to others 
i^^tJlTRS^'^ to £apAo7*iBceffl. Mr. Hut- 
ton discovered one of these Stigmarise forming 
a huge dome-shaped body, from which twelve 
branches spread horizontally in all directions, 
each, usually dividing into two arms, from twenty 
• lAoAXtj, FoM. Flora, p. 166. 



<ai.XX3 OF THB GOAL 8TEATA. 433 

to thirty feet long, to which leaves of great length 
were attached. Dr. Buckland imagines these 
plants to have grown in swamps, or to have 
floated in lakes like the modem Stratiotes.* 

I shall postpone some general remarks on the 
climate of the Carboniferous period, arising out of 
the contemplation of its flora, until somethmg has 
been said of the contemporaneous Mountain lime- 
stone and its marme fossils. 

* Bridgew. Treat., p. 478. 



V S 



-.,• .. . 486. ^. >. 



f 



CHAPTER XXf, ^ 

CARBONIFEROtJS 4%R0UP COnHnued^ A1HD OLD RED,9ANDdTdNB. 

Corak and shells of the Mountain limestone — Hot dimate 
of the Carboniferous period inferred from the marine 
fossils of the Mountain limestone and liie pkmts of the 
Coal — Origin of the Coal-strata — Contemporaneous 
freshwater and marine deposits -— > Modem analogy cff 
strata now in progress in and around New Zealand — 
Vertical and oblique position of fossil trees in the Coal -^ 
How enveloped — How fiu* they prove a rapid rate of 
deposition — Old Red sandstone — its subdivisions — 
its fossil shells and fish. 

Carboniferous or Mountain limestone* — We 
have already seen that this rock lies sometimes 
entirely beneath the Coal-measures, while, in other 
districts, it alternates with the shales and sandstone 
of the Coal. In both cases it is destitute of land 
plants, and usually charged with corals, which are 
often of large size ; ^id several species belong to 
the lamelliferous class of Lamarck, which enter 
largely into the structure of coral reefs now grow- 
ing. There are also a great number of Crinoidea 
and a few Echinida, associated with the zoophytes 
above mentioned. The Brachiopoda constitute a 
large proportion of the Mollusca, many species 
being referable to two extinct genera, Spirifer (or 



cb.xxw 



HOCMTAIK £lMBSrON& 



437 



Spirifera) (Fig. 264.) and Producta (Fig. 265.). 

There are also many univalve and bivalve shells 

fig. 564. Pig. ses. 




of existing gmera in the Mountain limestone, 
such as Turritella, Buccinum, Patella, Isocardia, 
Nucula, and Pecten.f But the Cephalopoda de- 
part, in general, more widely from living forms, 
some being generically distinct from aU those 
found in strata newer than the CoaL In this 
number may be mentioned Orthoceras, a siphun- 
cled and chambered shell, like a Nautilus uncoiled 
and straightened. Some species of this genus are 
several feet long (Figs. 266, 267.). The Gonia- 
Bg. 266. Fig. 267. 




tite is another genus, nearly allied to the Ammon- 
ite, from which it difers in having the lobes of 

•> PhiUipa, OeoL of Yorkah. pi. 10. fig. II. 
f Ibid., pi. 8. fig. 19. I Ibid., vol.ii. p. 208. 

V 3 



438 CLIHATE OF THE CPatH. 

die septa free from lateral demiculations, or ere- 
natures; bo that the outliae of these is continiunu 
and iininteTTt^tted (see a, Fig. 268.). Their 
siphon is small, and in the form of the strise of 
growth they resemble NautilL Another extinct 
generic form of Cephalopod, abounding in ^e 
Mountain limestone, and not fomid in strata of 
later date, is the Bellerophon (Fig. 269.), of 

Fig. S68. a Kg. 969. 




If ounttdn Braeatoiw. 

which the shell, like the living Argonaut, was 
with<)ut chambers. 

Climate of the Carboniferous period. — The abun- 
dance of lamelliferous and other corals, of large 
chambered C^halopods and Crinoidea, naturally 
lead us to infer that the waters of the sea, at this 
period, were of a &r warmer and more equable 
temperature than is now experienced in diose 
latitudes where the Coal strata abound, in Europe. 
M. Adolphe Brongniart has been led to a similar 
conclusion in regard to die temperature of the 
air, from considering the Carboniferous flora. 

• Phillipg, OeoL of Yorkdi., pi. 2a fig. 65. 
+ Ibid., pi. 17. fig. 15. 



Ch. XX13 CABBOVIFBROUS FBRIOIX 480 

Hie unquestioned existence of large tree-ferns, 
such as Caulopteris (Fig. 251.), now exclusively 
the inhabitants of hot and humid climates, and 
the great variety of fossil fronds of ferns in the 
Coal confirm this idea, even if we refuse to accede 
to the ai^uments adduced to prove that Sigillar* 
rise were tree-ferns of extinct genera. The same 
views receive ferther countenance, if the Lepido- 
dendra and Calamites are rightly conjectured to 
have been gigantic plants of the orders Lycopodi" 
acetB and EquisetacecB^ which, although most largely 
developed at present in the tropical zone, are 
even there of pigmy stature in comparison with 
the fossil tribes just alluded to. The Araacaria, 
also, is a family of pines. now met with in temper- 
ate and warm latitudes ; and the fir trees proper 
to the forests of arcdc regions do not appear to 
have any fossil representatives in the Coal. M.. 
Ad. Brongniart, when endeavouring to establish 
the great heat and moisture of the climate of the 
era imder consideration, may perhaps have relied 
too much on the numerical preponderance of 
ferns over other orders of coal-plants. We may 
easily be deceived by such reasoning, because it is 
founded on negative facts, or the absence of plants 
of certain orders, &milies, and genera. On this 
subject Professor Lindley has observed, that the 
small variety in the forms of each fossil flora 
must, in a great degree, depend on the relative 

u 4 



imtrm$Sb$tity of plants when suspended' In wacefr- 
bcafiKe they are imbedded in Btxata* In* iIIudtSrA^ 
lion of this pdint^ he threw into a teasel contain*'' 
iag tmtk water 177 jdantB, among which weite spe- 
cies of all the orders found in the Oarbonfferoii^ 
Ibra, with others representing the remaining 
fiunilieB and natural orders in the living creation, 
and found that, at the end of two years, s3l had 
decayed and disappeared exc^t the ferns, palms, 
LyeopodtaoBf and Conifera* The fiructififcation of 
the ferns had also vanished, but the form and 
nervures of the leaves remained.* 

No inference, however, drawn from this eitpe^ 
riment, can entirely explain away^ the fact of the 
vast prepondecanoe in the coalnshales of fern^ 
leaves over those of Dicotyledonous plants. Im- 
pressions of these last, together with their wood,' 
are plentifully preserved in tertiary rocks in 
which fossil ferns are rare; and had they been 
drifted down in as large numbers as ferns into' 
the estuaries of the Carboniferous period, they 
would have left impressions of their shape in 
shale and sandstone, as they have done in more 
recent formations. 

It would, moreover, be rash to assume that the 
coal-plants in general floated about in water for a 
year or two before they were enveloped in sedi- 

* Lindley, Foss. Florae part 17. 



» 

f 

I! 

E 

i 

i 

r 
i 



tlieni ,if1^re< (deposij^ inftzudiatdy wkh the omitd^ 
ai)L4 v^wd 8i¥9pt; €l9¥?n with them' by riVerSMXitb^ 
la^^r.^tbe ooiu This must baVe<kB^)eiae€i ;^»^ 
tlw^^e jBairecase». where the: feniis^till retmn.^their ' 
fip^<3^fic»tion. Wher^ithi9 has disappettped, its' 
d9fX9»pQ8ition may o^n haye been subsequent. to ' 
th(^ind^sure of the firond in mud or sand, ; 

Origin of the Coal strata. — • iPetached porlions • 
of the aaeient Carbonifi^rous git)up extend firom^* 
Gkffitral Europe to Melville Island and the Con* 
fines of the arctic region^ but. do not appear in the 
south of Europe; for the lignite and coal found 
south of the Alps and Pyrenees, in %)ain9 Italy$ 
Greece, and other countries bordering the Medi*- 
terranean, seem referable to the Cretaceous and 
other comparatively modem groups. 

It has been already shown that, in some parts 
of England) as in Shropshire, certain Coal-mea- 
sures consist of freshwater strata, and may have 
originated in a lake, while others, not far distant, 
were deposited in estuaries to which the sea ob- 
tained access occasionally; while a third class were 
formed at the bottom of an open sea, or in bays of 
salt wul^er into which land plants were drifted.* 

In .many parts of France and Germany there 
are isolated patches of Coal strata,, entirely free 

* Miirchi8op> Siluiiaa System^ p. 148. 

u 5 



442 ORIGIN OF THE [Twtn. 

£rom marine fossils, which repose on granite and 
other hypogene rocks. Th^ are often confined 
to an extremely small area, as at St Edeime, in 
the department of the Loire ; at Brassac, in that 
of Puy de Dome; at Sarrebruck; also in Silesia; 
and a hundred other places. All these deposits 
may have been formed in lakes, existing in the 
islands of that sea in which the Mountain lime- 
stone was formed.* 

If the climate of New Zealand and the sur- 
rounding ocean was warmer, so that tree-ferns 
could thrive more luxuriantly on the land, and 
corals build reefe in the sea, we might conceive 
new strata to accumulate in that part of the globe 
analogous to those of the ancient Coal. The two 
islands of New Zealand are between 800 and 900 
miles in length ; and through the middle of them 
runs a lofty chain of mountains, said, in some 
parts, to be 14,000 feet high, and covered with 
perpetual snow. Many rivers descend from their 
sides; and, in the spring, these are copiously 
charged with sediment, and with abundance of 
drift wood. Opposite the mouths of th^e rivers, 
and near the shores, wherever these may be 
wasting by the action of the waves, an irregular 
zone of gravel, sand, and mud, must be forming 
in the surrounding sea — a zcme several thousand 

* Burat's D'Aubuisson, torn. ii. p. 268. 



cat XXL] COAL STRATA. 443 

miles in circumference. No less than 57 species 
of ferns, some few of them arborescent, have been 
fjready discovered in this country ; and what is 
remarkable, one tree-fern ranges in this country 
as far south as the 46th degree, south latitude. 
There are no indigenous mammalia except one 
rat, and a species of bat; few reptiles, and none of 
large size; so that we may anticipate a total 
absence of the bones of land quadrupeds, and a 
scarcity of those of reptiles, in the modem estuary 
and lacustrine deposits of this region. That there 
are lacustrine strata now in progress is certadn, 
since one lake, called Rotorua, in the interior of 
the northern island, is said to be 40 miles long, 
and receives the waters of many small rivers and 
torrents. * 

The minor repetitions of alternate fresh and 
saltwater strata in the Coal, have been ascribed to 
such changes as may annually occur near the 
mouths of rivers ; but when shale and grit, con- 
taining coal and freshwater shells, are covered by 
large masses of coralline rock, and these again by 
otlier Coal-measures, we must suppose great 
movements of elevation and subsidence, like those 
by which I endeavoured to explain, in Chapters 
XVI. and XVIII., the superposition of the Cre- 
taceous group to the Wealden, or the altema- 

* Account of New Zealand, published for New Zealand 
Association. 

U 6 



<^tIoM' •of ai^koeoiK and caioireous rodcs'm 
ifae* Oolite. In adopting such views, weimist 
soppiwe the lapse of Tast periods of time ; aa tte 
thickness of the Coal strata, in some parts of Eng- 
land, independently of the Mountain limedtond, 
has been estimated at 9000 feet. Besides, ^re 
can hj no means presume diat all coal-^elds 'weriB 
in progress at once, much less that, in the same 
.field, each mass of strata which is parallel, or oc- 
cupies a corresponding level, was formed simul- 
taneously. It is &r more consistent with analogy 
to suppose that rivers filled up first one part of a 
fiord, gul^ or bay, nearest the land, and then an- 
(^er; so that the sea was gradually exduded firom 
certain spaces which it previously occupied. This 
is doubtless the cause why the coal-bearing strata 
are generally uppermost, and the Mountain lime- 
stone the lowest part of each series ; and why, in 
certain districts in the S. W. of England, the 
Mountain limestone suddenly thins out, so that 
coal-shales and grit rest immediately upon older 
and unconformable rocks. 

Erect position of fossil trees in the Coal strata* — 
A great number of the fossil trees of the Coal are 
in a position either oblique or perpendicular to 
the planes of stratification. This singular fact is 
observed on the Continent as well as in England, 
and merits great attention, not only as opening a 
curious field for speculation, but because it has 



IN nU fiOA,L. STRATA. . 



m6 



fiiroitihed KfM^ular ai^tunent to somewinteiStHilio 
denre to prove the eaith's orust to be ' nO' mate 
tbaa &000 or 6000 jiears old. The &ot did npt 
escape the notice of Wenier, who conceived thftt 
tbe trees mu»t have lived on the spots where thtfy 
are now &und fossil ; and this hypothesis waa de- 
fended by M. Alexandre Brongniart, in the a^ 
eomit given by him, in 1821, of the coal-mine of 
Treoil, at St. Etienne, near Lyons.* (Fig. 270.) 




In this mine, horizontal Coal strata are traversed 
by vertical trunks of Monocotyledonous vegetables 

* Annaki defl Iifon, I8S1. 



446 Baser position of tubes \jfmi 

resembling bamboos, or laige Equiseta. These 
beds are represented in the above figure (270.), 
and are firom 10 to 13 feet in height, consisting of 
micaceous sandsUme, distinctly stratified, and 
passing into the slaty structure. Since the con- 
solidation of the stone, there has been heare and 
there a sliding movement, which has broken the 
continuity of the stems, throwing the ujqier parts 
of them on one side, so that tli^ are often not 
continuous with the lower. 

Now, had these trees, as some geologists con* 
tend, once formed part of a submerged forest like 
that of Portland, before described (see p. 353.), 
all the roots would have been in the same stratum, 
or would have been confined to certain levels, and 
not scattered irregularly through the mass. Be- 
sides, when the stems have any roots attached to 
them, which happens but rarely, they are im- 
bedded in sandstone precisely similar to that in 
which the trunks are inclosed, there being no soil 
of di£Perent composition like the Portland dirt- 
bed, — no line of demarcation, however slight, be- 
tween the supposed ancient surface of dry land 
and the sediment now enveloping the trees. 

Some may, perhaps, think it superfluous to ad- 
vance such objections to M. Brongniart's theory, 
since Dr. Buckland has informed us that, when he 
visited these same quarries of Treuil in 1826, he 
saw so many trunks in an inclined posture, that 



ch. xxu m TUB COAL stuata. 447 

the occasional verticality of others might be ao« 
cidental.* Nevertheless, the possibility of so many 
of diem having remained in an upright posture 
demands explanation; and there are analogous 
cases on record respecting similar fossils in Great 
Britain of a still more extraordinary nature. 

In a colliery near Newcastle, say the authors of 
die Fossil Flora, a great number of SigiUarias 
were placed in the rock as if they had retained 
the position in which they grew. Not less than 
dO, some of them 4 or 5 feet in diameter, were 
visible, within an area of 50 yards square, the 
interior being sandstone, and the bark having 
been converted into coal. The roots of one indi- 
vidual were found imbedded in shale ; and the 
trunk, after maintaining a perpendicular course 
and circular form, for the height of about 10 feet, 
was then bent over so as to become horizontal. 
Here it was distended laterally, and flattened so 
as to be only one inch thick, the flutings being 
comparatively distinct.-}* Such vertical stems are 
familiar to our miners, under the name of coal- 
pipes. One of them, 72 feet in length, was dis- 
covered, in 1829, near Gosforth, about five miles 
from Newcastle, in coal-grit, the strata of which 
it penetrated. The exterior of the trunk was 
marked at intervals with knots, indicating the 

♦ Bridgew. Treat., p. 471. 

f Lindley and Hutton, Fobs. Flo., part 6. p. 150. 



mi 



ERBCX: ;^^JTU>;ii OE, T9X9B 



PS^^-) 



pokite fl which biwches had shot oC , 1^ "wgq^, 
of ,the interior had been convjarted iioo c^Kimate^,. 
of lime; and its structare was beaiiriiy l|y ^l^wf;^ ., 
by cutting transverse slices, ao thin as tp ]}ejxm^ 
parent (See p. 82.) 

In 1830, a slanting trunk was expos^ ii^ r 
Cndgleith quarry, near Edinburgh, the total 
length of which exceeded 60 feet. Its diamet^ 
at the top was about 7 inches, and near the base 
it measured 5 feet in its greater, and 2 feet in its 
lesser width. The bark was conyerted into a 
thin coating of the purest and finest coal, forming 
a striking contrast in colour with the white quart- 
zose sandstone in which it lay. The annexed 




JmcUnedpoUtion qf a/o$$il tree cuttutg through horixontal beds qf *and$ione, 
Craigleith quarry, Edinburgh. Angle of inclinatioii from a to ft S7^. 

figure represents a portion of this tree, about IS 
feet long, which I saw exposed in 1830, when aU 
the strata had been removed fi:t)m one side. The 
beds which remained were so unaltered and un- 
disturbed at the point of junction, as clearly to 
show ' that they had been- tranquilly dqioffited 



Ch.'XXvi IK THE COAL ST&ATA. 4!^* 

roiUid th^ tree, and that the tree had not Biib^ 
se^uently pierced through tliem, while they 'i^ere 
yet in a soft state. They were composed chiefly 
of silieeoiis sandstone, for the most part white; and 
divided into laminae so thin, that &om six to four-* 
teen of them might be reckoned in the thickness 
of an inch. Some of these thin layers were dark, 
and contained coaly matter ; but the lowest of the 
intersected beds were calcareous. The tree could 
not have been hollow when imbedded, for the in- 
terior still preserved the woody texture in a per- 
fect state, the petrifying matter being, for the 
most part, calcareous. * It is also clear, that the 
lapidifying matter was not introduced laterally 
from the strata through which the fossil passes, as 
most of these were not calcareous. It is well 
known that, in the Mississippi and other great 
American rivers, where, thousands of trees float 
annually down the stream, some sink with their 
roots downwards, and become fixed in the mud. 
Thus placed, they have been compared to a lance 
in rest; and so often do they pierce through the 
bows of vessels which run against them, that they 
render the navigation extremely dangerous. But 
the vertical coal-plants did not always retain their 
roots* Perhaps they sank with their larger end 
downwards, because the specific gravity of the 

* 8ee fignres of texture, Witham, Foss. Veget., pi. 3. 



4S0 iK'^'B OF iMvoamow ptetn. 

wood may have bem greatest near die lower end 
In treesof the Endogenons class, in particular, the 
wood of the inferior and older part of the trunk 
is more dense than the upper and younger pot^ 
tions ; and if the former should become water- 
logged while the uj^r part of the stem still 
remained nearly as light as water, or evea lighter, 
not only would the whole trunk descend perpen- 
dicularly, but when it reached the bottom it 
might stand upright, provided a very slight sup- 
port was afforded to its lower extremity by pene- 
trating to the depth of a foot or two into soft mud 
How long such trunks, if constantly submerged, 
might resist decomposition, is a question which 
cannot, perhaps, be determined; but, judging 
from the duration of wooden piles constandy 
covered by water, and trees naturally submerged, 
like those in Louisiana*, we may conclude that 
they might endure for many years, so tiiat their 
envelopment in strata, like those of the Coal, may 
have been effected without a very rapid rate of 
deposition. 

If, however, we assume that strata 30 or 40 
feet thick were often thrown down in a few years, 
months, or even days, tiiis fact affords no ground 
for calculating the time required for the formation 
of a wide coal-field. 

* See Principles, Index, ** Bistineau.*' 



Cb. XXI J OP THS COAI# STRATA. A5i 

Suppose, for example, the structm'e of a eoal* 
fidd always resemUed diat exhibited in the an- 
nexed section (Fig. 272.), we might then infer, 
that if the lowest set of strata, a, having a thick- 
ness of fifty feet, required half a century for its 
acciunulation, the strata, a, 6, c, constituting the 
entire coal-field, and being 150 feet tinck) 

Fig. 272. 

I i I 

might have been completed in a century and 
a half. But as the beds are wedge-shaped, 
and often thin out ; and as the successive bediB 
of a single coal-field are usually arranged in the 
form of ^, bf c, d, e (Fig. 273.), we cannot calculate 

Kg. 27S. 




their number from considering any one section. 
The deposits, a, i, c, d, e, traced in a given direc- 
tion, may have taken each fifty years for their 
deposition ; but they may have been as limited in 
breadth as in length. They may have constituted 
originally a narrow strip of land like part of the 
delta formed by the Mississippi, since New Orleans 
was built, by the incessant discharge of mud and 
drift timber into the Gulf of Mexico. Although 
by this means a narrow tongue of land has been 
made to protrude for several leagues into the sea, 
yet thousands of years may elapse before a square 



area of Ifl^ bud, haTitig a diasmeter- of as manj 
laagttefl^ can be gained firom the €hilf of Mexico. 

OLD BSD SAHDSTONB. 

: It was slated that ^le Garbonilmras ibrmatton 
wv suniHnmted by one cidled the ^^New Bed 
Sandstone^'' and underlaid by another called the 
Old Red, which last was formerly merged in the 
CarlMMii£»oii8 system, but is now fbmid to be dis- 
tiBgaishable by its fossSs. The Old Red Sand- 
atone is of enormous thi^siess in Herefordshire^ 
Worcestershire, ^iropthire, and South Wales, 
where it is seen to crop out firom beneath the 
Coal-measures and to repose upon the Sflurian 
rocks. In that rf^on its thickness* has been es* 
timated by Mr. Murchison at no less than 10,000 
feet. It consists there of 

lit A quartHMe ^onglomente paasiag downwanb into dioc<- 
olate-red and green sandstone and marl. 

2d. Cornstone and marl (red and green argillaceous spotted 
nrnda, .with irregular coufMs of impure coacietioDarjr 
limestone, pronacially caUed Comatone, mottled, red, 
and green ; remains of fishes). 

Sd. Tilestone (finely laminated hard reddUh or green mics- 

eeouB or qiwrfaoses«ttdatDii«s,irhicfa spHt into tiles; »- 
mains of moUusca and fishes). 

I have already observed that fossils are rare m 
marls and sandstones, in which the red oxide of 
iron prevails; in the Cornstone, however, of the 
counties above-mentioned, fishes of the genera Ce- 



p}ialaspis a;^d Qucbus \^ye heisn digcoyeri^dL* in 
th« Ti]^tgmos. also, Icthyodorulitesy of thegeniU 
Onchusy have been obtained ; and a species of Dip* 
terus, with moUusca of the geneora Avicula, Area, 
CucuUa^ Terebratula, Lingula, Turbe» Trochus, 
fT^Tritella, Bellerophon, Orthooeras,aQdother£k)*« 
... By consultinggeologijcal maps, the reader wUl 
pserceiv^ that from Wales to the north' of Scotland^ 
the Old Red sandstone appears in patches, and 
often in large tracts. Many fishes have been 
found in it at Caithness |, and various organic 
remains in the northern part of Fifeshire, where 
it crops out from beneath the Coal formation, and 
q>reads into the adjoining southern half of Forr 
farshire ; forming, together with trap> the Sidlaw 
hills and valley of Strathmore. ( See section, p. 99. ) 
A large belt of this formation skirts the south- 
ern borders of the Grampians, from the sea^coast 
at Stonehaven and the Frith of Tay to the opposite 
Western coast of the Frith of Clyde. In Forfarshire, 
where, as in Herefordshire, it is many thousand feet 
thick, it may be divided into three principal mass- 
es : 1st, redand mottled marls, cornstoneand s^d- 
•tone ; 2d, Conglomerate, often of vast thickness ; 
3d, Tilestones and paving stone, highly micaceous, 
and containing a slight admixture of carbonate of 

♦ Murchison*s Silurian System, p. 180. f Ibid., p. 183. 
X See Geol. Trans. 2d series, vol. iii. plates 15, 16, 17. 



lime. (See section, p. 99.) In the uppermost of 
these divisions, but chiefly in the lowest, die re- 
mains of fish have heen found, of the genus named 
by M. Agassiz, Cephalaspis, or buckler-headed, 
from the extraordinary shield which covers the 
head, and which has of^ been mistaken tor that 
of a trilobite, of the division Asaphus. (See Fig. 
276. p. 459.) 

Kg. S74. 




CrfUaipit Lftlbi, Agut. Lanfth ^ Incbw. 
T^it fig^ire is froa a tpeamai now in ny tallteliim, wliich I pn- 
airtd at Glammiti, m Fiyrfarifurt see otfaer figures, Agaisu, 
Tol. ii. Tab. I. a. & I. b. 

a, one of the peculiar HCates with which the head a corersd 
when perfect. TheK scales are genenJlj removed, as in the spe- 
cimen above figured^ 

b, c, scales from different parts of tfae bod; and taiL 

A gigantic species of fish of the genus Gyrolepis 
has also been found by Dr. Fleming in the Old 
Red sandstone of Fifeshire.* 

• See AgABsiz, Poieaona Fossiles, torn. ii. p. 139, 



455 



CHAPTER XXII. 

PRIMARY FOSSILIFEROUS STRATA. 

Primary Fossiliferous or Transition Strata — Terra ** Grau- 
wack^*' — Silurian Group — Upper Silurian and Fossils — 
Lower Silurian and Fossils — Trilobites — Graptolites — 
Orthocerata — Occasional horizontality of Silurian Strata 
— Cambrian Group — Endosiphonite. 

We have now arrived in the descending order at 
those more ancient sedimentary rocks, which I 
have called the Primary Fossiliferous (see p. 268.)> 
and to which Werner first gave the name of 
Transition, for reasons fully explained and dis- 
cussed in the 12th chapter. Many geologists have 
also applied to these older strata the general name 
of " grauwacke," by which the German miners 
designate a variety of quartzose sandstone, which 
is usually an aggregate of small fragments of 
quartz, flinty-slate (or Lydian stone), and clay- 
slate, cemented together by argillaceous matter. 
But far too much importance has been attached to 
this kind of rock, as if it were peculiar to a certain 
epoch in the earth's history, whereas a similar 
sandstone or grit is not only found sometimes in 
the Old Red, and in the millstone grit of the 
Coal, and in certain cretaceous formations of the 
Alps — but even in some tertiary deposits. 

In England, the Old Red sandstone has been 



456 PRIMARY lOttliifffilKKW STRATA. [PM IL 

generally regarded as the base of the secondary 
series ; but by some writers on the Continent, the 
Old Red and Coal formations have been classed as 
the upper members of the Transition s^ies, a 
method adopted by Dr. Buckland, in his late 
Bridgewater Treatise. This classification^ how- 
ever, requires us to draw a strong line of demarc- 
ation between the Coal and the lower New Red 
sandstone group, which now that the fossils of these 
two groups are ascertained to be very analogous, 
becomes a more €urbitrary division than that which 
separates the Old Red from the uppermost of the 
primary fossiliferous. strata. 

Professor Sedgwick and Mn Murchison. have 
lately proposed to subdivide all the English sedi- 
mentary strata below the Old Red sandstone into 
two leading groups, the upper of which may. be 
termed the Silurian, and the inferior the Cambrian 
system. Mr. Murchison has applied the name of 
Silurian to the newer group, because these rocks 
may be best studied in that part of England and 
Wales which was included in the ancient British 
kingdom of the Silures. He has also formed four 
subdivisions of the Silurian system, which he has 
designated as the Ludlow, Wenlock, Caradoc, and 
LlandeilQ, indicating thereby the places where the 
prevailing characters of each formation are most 
perfectly exhibited. The following Table explains 
the succession of these deposits.* 

* See Morchijson's Silurian System. 



9^^,^nj 



HUmUKIAV 



467 



u. 








g 
•a 

g 
§ 



.^ CO 




I 
•I 

is 
I 

8 

04 



I 



S 
1 



o 

■s 

5 



»3 



II . 



« b 

s 



S s 
^.1 



15 . 

O V 



^ 






6 



^ 






I 



ll 

3" 



§ 



1'^ 



C3 S 

o>«8 



01 



8 
O 

II 



w 



si 



45B iTVpn m.ottU]f tocKs ti^n 

UPPER SILURIAN B,OCkB. 

Ludhw formation. — ». Xhls member df the upper 
l^urian group, as Will be seen by the above table, 
is of great lliickiiei^ and subcfivltted' into three 
puts. Each of these may be dQstMguished near 
the town of Ludlow, and at oth^ ^ad^ in Bhrop- 
shire and Hereford^ur^ by peculieo* organic re- 
makis.. The mosijjftmarkable fossils af 6 the scales, 
idithyodorulites, jaws^ teedi, and coprolites of fish, 
of the uppei* Ludlow rock,* As they sjte Ae 
oldest remains of y^tebrated animals yet known 
to geologists, it Is worthy of notice that they 
bdiong to fish of a high or Very perfect orgalu- 
zatioiL 

Among the fossil shells are spedes of leptastj^ 
cf this, terebratula, avicula, trochus, orthoceras, 
bellerophon, and others.f 

Fid* 275. 




TerOraMa WtHont't Sow. ImcBow ftormatioiu 

Several species also of trilobite, an extinct 
species of crustacean, characteristic of the Silurian 
period in general, are found in the lower Ludlow 
limestone. Those r^resented ki the annexed 
fibres, Calymem Blumenbachii and jisaphus cau^ 

* Murcbison^ Silurian System, p. 198, 199. f Ibid. 



Ck. rxni AVD THEIR Fosnta 45S 

datusf are common txi Has limestone, and to the 
Wenlock formation whicb succeeds next in the 
descending order. 

Fig. *76. Big. 977. 




BnjunUrt^ea 



S<Hne of the Upper Ludlow sandstones are 
rii^le-mai-ked, thus affording evidence of gradual 
deposition ; and the same may be said of the fine 
argillaceous shales of tlie Ludlow formation, which 
are of great thickness, and have been provincially 
named ** mudstones," from their tendency to dis- 
solve into mud. In these shales many zoophytes 
are found enveloped in an erect position, having 
evidently become fossil on the spots where they 
grew at the bottom of the sea. Among others, the 
graptoUte is abundant. (See p. 462.) The facility 
with which these upper Silurian shales, when ex- 
posed to the weather, are resolved into mud, 
proves that, notwithstanding their antiquity, they 
are nearly in the state in which they were first 
thrown down at the bottom of the sea. All rocks, 
therefore, of the transition era of Werner, were 
not originally precipitated in a semi.«rystalline 
state as was formerly pretended. (See p. 260.) 
X 2 




1^ tontaining the large firilo- 
bites Ataphus Bvckii (F^. 
^^Q.),waA4•^yram$.* There 
are also several genera of mol- 
lusca in this deposit, and it 
is an interesting &ct, that with 
many extinct forms of testacea peculiar to the 
lower Silurian rocks, such as orthoceras, penta- 
raerus, spirifcr, and productus, others are asso- 
ciated belonging to genera still existing, as nau- 
tilus, turbo, buceiiium, turritella, terebratula, and 
orbicula.f 

No land plants seem yet to have been disco- 
vered in strata which can be unequivocally demon- 
Btrated to belong to the Silurian period. 

In Norway and Sweden the Silurian strata 
extend over a wide area, and so much resemble 
those of England in litfaolt^csl character and 
fossils, that they will probably be found to be 
divisible into similar groups. They are composed 
of lat^ deposits of sandstone, which is sometimes 
found at the base of the system, resting on gneiss 
and calcareous rocks, with orthocerata and corals ; 
the chain-coral, {Fig. 278.) before mentioned, being 
very conspicuous ; also &ie bituminous shales con- 
taining graptolites. (Fig. 260.) 

These bodies are supposed by Dr. Beck, of Co- 
penhagen, to be fossil zoophytes, related to the 
• Murchiaon, Silurian System, p. S2fi. f Ibid. p. 351. 



<a. XZII.] HOtEKnTAL fllLDBIAS STRATA. 




punion DTilie iMl at n. ng. M-, nManl aiil!, •iMKiiu 
the tube uid Ita mOi irithla thet^iADiictei 



Sffurunt ffm&i oeeatitmaliy horitantal. — The Si- 
lurian strata throughout a large part of the pro- 
vinoe of Skaraborg, in the south of Sweden, are 
perfectly horizontal; &e different eubordinate 
formations of sandstone, shale, and limeBtone, 
occurring at corresponding heights in hiJls many 
leagues distant from each other, with the s»ne 
)nin«^ characters and organic remains. It It 
dear tliat they have never been disturbed since 
the time of their depoution, except by such gn* 
dual movements as those l^ which large areas in 
Sweden and Greenland are now slowly and in- 
sensibly riuBg above or sinking bdow their former 
X 4 



4i4 Bomaommu mnmmMM (MmuiTA. (rmin. 

letd- Tfai^ anaieiit fimestone and ilitiW dao of 
die Canadian lake district before mentioned, are 
for the most port horizontaL 

Tbeae &ctB are very important, as the more 
aneicnt rocks are nsoaUj much distii]l>ed» and 
faoriaontality is a ccHmuon dnracter of never 
strata. Similar excepti<ms, howerer, oocor in re- 
gard to the more modem or tertiary formfttinitt 
which, in some places, as in the A^ps, are not 
only Terdcal, but in a reversed positionL These 
appearances accord best with the theory which 
teaches that, at all periods, some parts of the 
earth's crust have been convulsed by violent move- 
ments, which have heea sometimes continued 80 
long, or so often repeated, that the derangement 
has become excessive, while other spaces have es- 
caped agcun and again, and have never oiice been 
visited by the same kind of movement. Had 
paroxysmal convulsions ever agitated simultane- 
ously the entire crust of the earth, as some have 
imagined, the primary fossiliferous strata would 
nowhere have remained horizontaL 

Cambrian Group* — Below the Silurian strata in 
the r^on of the Cumberland lakes, in N. Wales, 
ComwaU, and other parts of Great Britain, there 
is a vast thickness of stratified rocks, for the most 
part sla^, and devoid of fossils. In some few 
places a lew organic remains are detected spe- 
cifically, and some of them generically, distinct 



frfim UioB^ <rf the Sihirian poriod. llufte radw 
have been' called Cambrian by' Frofeeaor Sedgwid^ 
because they are largely deTd(^>M in N.^ Walosi' 
where they att^ a thickneea of sevtirgl tliousftnd 
y&rda, lliey are chiefly fonned of sla^ sand* 
Mone'aiid oonglomerote, in the midst of whi^ 
is a limestone otmt^niDg shells and cojsls, as at 
Bala in Merionethshire. A sla^ sandstone, foim- 
mg the bottom of the Cambrian system in Show- 
d(Hi, contains shells of the family Bracluopoda, and 
a. few zoophytes. * 

In some of the slate rocks of Cornwall, referred 
by Professor Sedgwick to the Cambrian group, 
cephalopoda of a very peculiar structure, called 
Endonphonites, have been detected, a form which 
appears not yet to have been observed in the Si- 
lurian formation. The siphuncle in this shell is 




■ Pfaillipa's Geology, Tol. i. p. IS9. Lardner's Cyclo]). 



f Camb. Phil. Trane. vol. vi. pi. 8. fig, S. 
X 5 



466 CAMBSIAV BCKK& C?Vl U 



▼entraly in whidi character it di&iB both from 
ammonite^ in which it is dorsal, and from natt« 
tilus, in which it is central, or nearly centraL 

Although the Cambriali group can scarcely yet 
be said to be established on the evidence of a dis- 
tinct assemblage of fossils, yet so great is the 
thickness of strata beneath the lowest of the well- 
determined Silurian rocks, all of a date posterior 
to the creation of organic beings, that we may 
reasonably expect to be able to divide the primary 
fossiliferous strata into two groups. 



4OT 



CHAPTER XXin. 

ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS« 

Tests of relative age of volcanic rocks — Test by superpo- 
sition and intrusion — By alteration of rocks in contact 
-—Test by organic, remains — Test of age by mineral 
character — Test by included fragments <— Volcanic rocks 
of the Recent and Newer Pliocene periods — Miocene — 
Eocene — Cretaceous — Oolitic — New Red sandstone 
period — Carboniferous — Old Red sandstone period — 
Silurian — Upper and lower Cambrian periods — Relative 
ages of intrusive traps. 

Having referred the sedimentary strata to a long 
succession of geological periods, we have next to 
consider how far the volcanic formations can be 
classed in a similar chronological order. The tests 
of relative age in this class of rocks are four : — 
Ist, superposition and intrusion, with or without 
alteration of tlie rocks in contact; 2d, organic 
remains; dd, mineral character; 4th, included 
fragments of older rodos. 

Test by superpositioTi^ 8fc. — If a volcanic rock 
rest upon an aqueous deposit, the former must be 
the newest of the two, but the like rule does not 
hold good where the aqueous formation rests upon 
the volcanic, *for we have already seen (p, 181.) 

X 6 



466 TBTTS OF MMLATtVB AOE fBut IL 

tJMt melted matter, rising fitsm below, may pkne- 
trate a sedimentary mass witboni leadhing die 
surface, or may be forced in ocmfermaUy between 
two strata, as & at n in the anneaced figure 
(Fig. 284.), after which it may cool down and con- 
solidate. Superposition, therefore, is not €^ the 

Hg. 284. 

D 




'7fF^^'^.'..^^'.'^'.' r^TTT^ 



same value as a test of age in the imstratified vol- 
canic rocks as in fossiliferous formations. We can 
only rely implicitly on this test where the volcanic 
rocks are contemporaneous, not where diey are 
intrusive. Now they are said to be contranpo- 
raneous if produced by volcanic action, which was 
going on simultaneously with the deposition of the 
strata with which they are associated. Thus in 
the section at d (Fig. 284.), we may perhaps ascer- 
tain that the trap b flowed over the fossiliferous 
bed c, and that, after its consolidation, a was depo- 
sited upon it, a and c both belonging to the same 
geological period. But if the stratum a be altered 
by b at the point of contact, we must then conclude 
the trap to have been intrusive, or if, in pursuing 
b for some distance, we find at length that it cuts 
through the stratum a, and then overlies it. 



Ch. XXIIL] 



OF YOLCaSriO AOCiEfi. 



469 



We may, hoi^ever, be easily deceived in mp- 
posing a volcanic rock to be intrusive^ when in 
reaJity it id cont^Bporaneoiis, for a sheet of lava, 
as it st>reads over the bottom of the sea» cannot 
rest every where upon the same stratum, either 
because these have been denuded, or because, if 
newly thrown down, they thin out in certain places, 
thus allowing the lava to cross their edges. Be- 
sides, the heavy igneous fluid will often, as it moves 
along, cut a channel into beds of soft mud and 
sand. Suppose the submarine lava f, to have come 
in contact in this manner with the strata a, &, c, 
and that, after its consolidation, the strata d, e^ are 
thrown down in a nearly horizontal position, yet 
SO as to lie unconformably to f, the appearance of 
subsequ^it intrusion 
will here be complete^ 
although the trap is 
in fact contempora^ 
neous. We must, un- 
less we find the strata 
c? or e to have be^i altered at their junction, as if 
by heat, not therefore hastily infer that the rock f 
is intrusive. 

When trap dikes were described in the 8th 
chapter, they were shown to be more modem than 
all the strata which they traverse. The ninety- 
fathom dike in the Northumberland coal-field 
(see section, Fig. 286.), passes through coal mea- 



Fig. 285. 




4T» 



TBBtS OF RBLAnTB AGE 



(Fiitll. 



sioreB whidi are mudi distuibed.* The beds of 

Ttg. 286. 




Cog. 



Pike. 
Seotim M • giwry ^ <Mlerootiti,i^i1kumbai fam/. 



overljring Magnesiaa limeBtone are not cut through 
by the dike, but appear to be in the position in 
which they were originally deposited in a hollow, 
existing in the denuded surface formed by the 
carboniferous strata and intrusive dike. Now here 
the coal-measures were not only deposited, but had 
been fissured before the fluid trap was introduced 
to form the dike. It also appears by the truncated 
edges of the Coal strata, and the abrupt termination 
of the dike on which the Magnesian limestone 
rests, that denudation had taken place at a period 
intervening between the injection of the volcanic 
matter and the deposition of the Magnesian lime* 
stone. Even in this case, however, although the 
date of the volcanic eruption is brought within 
narrow limits, it cannot be defined with precision ; 
it may have happened either at the close of the 
carboniferous period, or early in that of the lower 
New Red sandstone, or between these two periods, 

* See Mr. Winch's account, GeoU Trans. 1st ser. vol. iv. 
p. 1. 



Ob. XXniJ top VOLCARIC BOCKS. 471 

when the state of the animate creation, and the 
physical geograj^y of Europe were gradually 
changing frcnn the type <^ the carboniferous era t9 
that of the lower New Red formation. 

In regard to all stratified v<dcanic toffi;, the test 
of age by superposition is stricdy applicable to 
them, according to d:ie already explained rules in 
the case of other sedimentary deposits* (See 
p. 272.) 

Test of age by organic remains. — We have seen 
how, in the vicinity of active volcanos, scoriae, 
pumice, fine sand, and firagments of rock are 
thrown up into the air, and then showered down 
upon the land, or into neighbouring lakes or seas. 
In the tuffs so formed, shells, corals, or any other 
durable organic bodies which may happen to be 
strewed over the bottom of a lake or sea will be 
imbedded in tufi^, and thus continue as permanent 
memorials of the geological period when the vol* 
canic eruption occurred. Tufaceous strata thus 
formed in the neighbourhood of Vesuvius, Etna, 
Stromboli,and other volcanos now active in islands 
or near the sea, may give information of the re- 
lative age of these tuffi at some remote future 
period when the fires of these mountains are ex- 
tinguished. By such evidence we can distinctly 
establish the coincidence in age of volcanic rocks, 
and the different primary, secondary, and tertiary 
fossiliferous strata already considered. 



4gti TEwi ffif, ^»^vm AftB . i;?^!!. 



] THe t^ OQW aUiiided to ^are /^ot ^a^liigj^^, 
ipiiiii€^ but include, in some i^aces» freflliiiqwtpr< 
aballuH in oibeni» the. bones of teireatrial qwn 
drupeds. The diversity of organic. VQinaiiiSiia 
filMnalioaB of this namre is perfect! j int^lijgibl^ 
if we reflect on the wide dif persion of ej^pted 
laatter during late eruptions, sudi as that of tb^ 
iNdeano . of Coseguina, in the province of Nie^ 
ragua, January 19. 1835. Hot cinders and .fine 
sconce were then cast up to a vast height, and 
covered the ground as they fell to the Aepiik 
of more than ten feet, and for a distance of 
dght leagues from the crater in a southerly 
direction. Birds, cattle, and wild animals were 
scorched to death in great numbers, and buried in 
these ashes. Some volcanic dust fell at Chiapa, 
upwards of 1200 miles to windward of the volcano, 
a striking proof of a coimter current in the upper 
r^^n of the atmosphere, and some on Jamaica, 
about 700 miles distant to the northreast In the 
sea also, at the distance of 1100 miles from the 
point of eruption. Captain Eden of the Conway 
sailed 40 miles through floating pumice, among 
which w^re.some pieces of considerably size.* 

Test of eye by mineral composition* — As sedi- 
ment of homogeneous composition, when discharged 
from the .mouth of a large river, is often deposited 

* Caldcleugh, PhU. Trans. 183C, p. 27., and Official Do- 
cuments of Nicaragua. 



olxxul] of voLCAiric vtoetM. 47^ 

simultettieoifsly oVeramdespiicey tio t pkrdGi^ltiid 
of Ikra flowing ffom 4 crater, dturing on^ ^n(pd(H^ 
imay^ spread over ah' extensive area, as in Iceland- 
in 1788, Wheii tiie melted matter, pouring fpom 
Skaptar Jokul, flowed in jstreatnsi in opposite di-^ 
rections, and caused a continuous mass, the ex^ 
treme points of which were BO miles distant froiri 
each other. This enormous current of lata varied 
in thickness from 100 feet to 600 feet, and in 
breadth, from that of a narrow river gorge to 1ft 
miles.* Now, if such a mass should afterwards be 
divided into separate fragments by denudation, we 
might still perhaps identify the detached portions 
by their similarity in mineral composition; Never- 
theless, this test will not always avail the geologist, 
for, although there is usually a prevailing cha^ 
racter in lava emitted during the same eruption, 
and even in the successive currents flowing from 
the same volcano, still, in many cases, the different 
parts even of one lava-stream, or, as before stated, 
of one continuous mass of trap, vary so much in 
mineral composition and texture, as to render 
these characters of minor importance when com- 
pared to their value in the chronology of the fossili- 
ferous rocks. 

It will, however, be seen in the description 
which follows, of the European trap rocks of dif- 

* See Principles, Index, ** Ski^tar Jokul." 



474 TWa^ OF BSI«AXIf8 A0E tBUtlL 

fartat age>» dnt ihey bud ofeen a peoviiar Ulhft* 
luteal charaoter» voseinUiuig tbe deferences befeiA 
remarked as exbdiig between tibe modem lavaaof 
Vcsavius, Etna, and Chili. (See p. IBS.) 

It has been remaxked that in Axerexgae^ the 
Eifel» and odier countries wbere trachyte and 
basalt are both present, the traoihytie rodks are for 
the most part older than the basaltic* These 
rocks do» indeed, sometimes aUemate partially, as 
in the y<doan0 of Mont Dor, in Auvergne ; bat 
the great mass of tradiy te oocupies in general an 
inferior position, and is cut dirough and over- 
flowed by basalt. It can by no means be in* 
ferred that trachyte {vedominated greatly at one 
period of the earth's history and basalt at another, 
for we know that trachytio lavas have been formed 
at many successive periods, and are still emitted 
from many active cratmrs; but it seems that in 
each region, where a long series of eriq)tions have 
pecurred, the more felspathic lavas have been first 
emitted, and the escape of the more augitio 
kinds has followed The hypothesis su^ested by 
Mr. Scn^ may, perhaps,* afford a solution of 
this problem. The minerals, he obsi^rves, which 
abound in basalt are of greater spedfic gravity 
tlian those composing the felspathic lavas ; thus, 
for example, hornblende, augite, and olivine^ are 
each more than three times the weight of water ; 
whereas common feli^r, albite, and Labrador 



fiilgpar, bave eacjki scarceljmore ifaan ^i timefiliifi 
ipeeific gravity cf water ; and the difference is i&^ 
ereased in consequence of there being much more 
iron in a metallic state in basalt and greenstone 
liian in trachyte and other felspatMc lavas and 
traps. If, therefore, a large quantity of rook b« 
melted up in the bowels of the earth by volcanio 
heat, the denser ingredients of the boiling fluid 
will sink to the bottom, and the lighter remain^ 
ing above will be first propelled upwards to llie 
surface by the expansive power of gases. Those 
materials, therefore, which occupied the lowest 
place in the subterranean reservoir will always be 
emitted last, and take the uppermost place on the 
exterior of the earth's crust. 

Test by include^ fragmenU.-^^Yie may sometimes 
discover the relative age of two trap rocks, or of 
an aqueous deposit and the trap on which it rests, 
by finding fi*agments of one included in the other^ 
in cases such as those before alluded to, where tbe 
evidence of superposition alone would be insuffl- 
cient. It is also not uncommon to find con- 
glomerates ahnost exclusively composed of rolled 
pebbles of trap, ajssociated witli stratified rocks in 
die neighbourhood of masses of intrusive trap. If 
the pebbles agree generally in mineral character 
with the latter, we are Aen enabled to determine 
the age of the intrusive rode by knowing that of 
the fi>ssiliferou8 strata associated with tlie ccmglo*' 



476 JDIFFEBEMT AGES QF [PaitIL 

merate. ' The origin of such conglomerates is e^r 
plained by observing the shingle beadies compbsed 
of trap pebbles in modem yolcanic islands, or at 
die base of Etna. 

Recent and newer Pliocene period. — I shall now 
select examples of contemporaneons volcanic rocks 
of successive geological periods, that the reader 
may be convinced that the igneous causes have 
been m activity in aU past ages of the world, and 
that they have been ever shifting the places where 
they have broken out at the earth's surface. One 
portion of the lavas, tuffs, and trap-dikes of Et&a, 
Vesuvius, and the island of Ischia, have been pro- 
duced within the historical era; another and a &r 
more considerable part have originated at times 
immediately antecedent, when the waters of the 
Mediterranean were already inhabited by the 
existing species of testacea. The submarine found- 
ations of Etna and Ischia have been upheaved to 
the great height of between 500 and 1500 feet 
above the level of the sea ; and the same observ- 
ations may be made respecting the base of many 
active volcanos which were first subaqueous vents, 
or, like Stromboli, half submerged, and then be- 
came subaerial, when the ancient bed of the sea 
was laid dry by elevation. 

Older Pliocene period* — In Tuscany and the 
Campagna di RoAia submarine volcanic tu£& are 
interstratified with the Older Pliocene strata of 



db.xxiiij VOLCANIC RocKa ^77 

the Subapeimine hills» in such a naaiiiier ^ td 
le^ye no doubt that they were the - product ^pf 
qruptions whidb occurred when the shelly uimU 
and sands of the Subapennine hills <were in ^ 
course of deposition. 

- Miocene period, — The most ancient volcanic 
rocks, consisting chiefly of trachjrte, of the Upper 
and Lower Eifel, are intercalated between Miocen? 
strata in such a. manner, as to prove them to have 
been coeval in origin. The eruptions, however, 
of the same district were continued down to th^ 
Newer Pliocene era, or were at least renewed .^S. 
that later period, so that showers of ashes from the 
Bhenish volcanos are interstratified with, the 
loess, in which, we have already stated, shells of 
land and freshwater species occur identical with 
those now living in Europe.* 

Eocene period. — The extinct volcanos of Ati- 
vergne and Cantal, in central France, commenced 
their eruptions in the Eocene period, but w^e 
most active during the Miocene era. In the 
lacustrine deposits, near tho^e ancient volcanos, 
the lowest strata were evidently formed befoi^e any 
eruptions had occurred. They consist of sandstone 
and conglomerate, containing rounded pebbles of 
quartz, mica-schist, granite, and other hypogene 
rocks, composing the borders of the ancient lakes, 

# See above, p. 297., and Principles, book iv. 



47i Y0ECABIC mocEB OP ttrntu, 

tet not die iliglilieBt in tfg i ninn r e of Taloaaie pfo- 
ddctB cin be detected. To Aese coiigloniefatei 
miiff<irflcd arffSDaoeom a»Mt calcBreons jumtIb cqii* 
eiiniiiE Eoeene sheUey dnzing the deptsilion of 
which some feeble signsof volcamcactaimfai^^ to 
ibour liMsautdytsk Above these^ freshwater marls 
and fimeetonee are seen fieqnentij to altemale 
with volcanic txtS^ and in diem some fixnls of die 
Uiocene pttiod are discovered. After die fiUing 
i3p or drainage of die ancient lakes, bi^ piles of 
trachytic and baaaltic rocki, widi volcanic breccias 
and eongkxnerateS) aecumidated to a duckness of 
several thoosand feet, and were supmmposed 
upon granite^ or die contiguous lacustrine stra&L 
The greater portion of diese igneous rodcs ^ 
pear to have originated during die Miocene period^ 
and extinct quadrupeds of diat era, bdonguig to 
die genera Mastodon, Rhinoc^Kis, and odiers, 
vnsre buried in ashes and beds of alluvial sand 
and gravel, which owe dieir preservation to sheets 
of lava which qiread over diem. 

Cretaceous period, — Aldiough we have no proof 
of volcanic rocks erupted in England during the 
deposition of the chalk and greennsand, it must not 
be supposed diat no dieatres of igneous acticm ex- 
isted in the cretaceous period. M. Virlet, in his 
account of the geology of tile Mctfea, (p. 1205.) 
has clearly shown that certain traps in Greece^ 
called by bun ophiolites, are of this date; as those^ 



for ef3tample, which idtemate con&irmsshly with cre- 
taceous limestone mid green-sand between Kastri 
and Damala in the Morea. They consist in great 
part of diallage rocks tttid serpentine^ and of an 
amygdaloid with calcareous kernels, and a base of 
serpentine. 

In certain parts of the Morea^ the age of these 
volcanic rocks is established by the following 
proo&: first, the lithographic limestames (see 
p. 3^) of the cretaceous era are cut through by 
trap, and then a conglomerate occurs, at Nauplia 
and other places, containing in its calcareous ce- 
ment many well-known fossils of tlxe chalk and 
greennsand, together with pebbles formed of rolled 
pieces of the same ophiolite, which appear in the 
dikes above alluded to. 

It was before stated that at Tercis^ near Dax, in 
the department of the Landes, in the south of 
France, highly inclined strata of limestone and 
marl occur, containing the fossils of the chalk, the 
inclined strata being in great part concealed by 
onconformaHe tertiary formations. In one section 
in this district I observed, alternating with thm 
layers of volcanic tuff, vertical cretaceous beds» 
which are perfectly conformable. Such tuffs were 
probably the product of submarine eruptions in 
the cretaceous sea« 

The traps of this country and of the neighbour- 
ing Pyrenees are generally opkitic, and many 



480 CBETACEOUS VOLCAHIC HOCKS. ^ l?VM\ 

Fig. S87. AdourR. JLu^B; Fay Arnt. 



Gihalft Mitf Mtomfc M|f In the auriram ^ JEkar. 
X. Inclined beds of chalk and conformable Tolcaiiic tuC 
a. h, e, d, Grayel, sand, and tertiary strata. 

# 

French geologists conceive them to be newer thao 
the cretaceous period, and therefore tertiary ; hut 
I know of no sections which demonstrate this 
point. M. Charpentier has argued that the ophites 
of the Pyrenees were more modem than all llie 
secondary strata of that chain, because in the con* 
glomerates constituting the upper part of the 
cretaceous series on the flanks of the Pyrenees, 
no rolled pebbles of ophite have been found* 
But this negative &ct may be explained by sup- 
posing that, in the cretaceous sea, which occupied 
the space where the Pyrenees now stand, the 
ophitic eruptions were submarine, and never 
formed islands or shoals exposed to denudation. 

The age of the trap of Antrim in Ireland, before 
described, as altering the chalk by its dikes 
(p. 176.), is uncertain. It is newer than the chalk 
of that region, which it cuts through and over- 
flows ; and, perhaps, it belongs to some one of the 
tertiary periods. As wood-coal and coniferous 
fossil trees have been found associated with it on 
the eastern shores of Lough Neagh, these plants 

♦ Cbaq)entier, Essai Geog. sur les Pyrantel, p. 524. 



Ch. XXniJ VOLCANIC ROCK& 4gl 

may hereafter throw light on this chronological 
qu^ation,^ 

iPeriod ofCMUe and Lias. — Although the green 
and serpentinous trap rocks of the Morea belong 
chiefly to the cretaceous era, as before mentioned, 
y0t it seems that some eruptions of similar rocks 
began during the oolitic period f ; and it is pro- 
bable, diat a large part of the trappean masses, 
ealldd ophicdites in the Apennines, and asso- 
oiated with the limestone of that chain, are of cor- 
responding age. * 

Whether part of the volcanic rocks of the 
Hebrides, in our own country, originated con- 
temporaneously with the lias and oolite which 
tl»y traverse and overlie, remains to be ascer- 
tained. 

Trap of the New Med sandstone period, — In the 
southern part of Devonshire, trappean rocks are 
associated with new red sandstone, and, accord-* 
ing to Mr. De la Beche, have not been intruded 
subsequently into the sandstone, but were produced 
by contemporaneous volcanic action. Some beds 
of grit, mingled with ordinary red marl, resemble 
sands ejected from a crater ; and in the stratified 
conglomerates occurring near Tiverton are many 
angular fragments of trap porphyry, some of them 
one or two tons in weight, intermingled with 

• Dr. Berger, Geol. Trans. 1st series, vol. iii. p. 188. 
f Boblaye and Virlet, Morea, p. 23. 

Y 



482 TRAP jCOKVAI. WITH 00 AL CWtU 

pebbles of other rocks. These angular fragments 
were probably thrown out from volcanic vents, and 
fell upon sedimentary matter then in the course of 
deposition.* 

CkarbomferofUA period, — Two classes of contem- 
poraneous trap rocks have been ascertained by 
Dr. Flelning to occur in the coal-field of the Forth 
in Scotland. The newest of these, connected with 
the higher series of coal-measures, is well exhibited 
along the shores of the Forth, in Fifeshire^ where 
they consist of basalt with olivine^ amygdaloid, 
greenstone, wack^, and tuff. They appear to have 
been erupted while the sedimentary strata were 
in a horizontal position, and to have suffered the 
same dislocations which those strata have subse- 
quently undergone. In the volcanic tufls of 
this age are found not only fragments of lime- 
stone, shale, flinty slate, and sandstone, but also 
pieces of coal. 

The other or older class of carboniferous traps 
are traced along the south margin of Stratheden, 
and constitute a ridge parallel with the Ochils, 
and extending from Stirling to near St. Andrew's. 
They consist almost exclusively of greenstone, 
becoming, in a few instances, earthy and amygda- 
loidal. They are regularly interstratified with the 
sandstone, shale, and ironstone of the lower coal- 

* De la Beche, GeoL Proceedings, No.41. p. 196. 



Ch. XXIII.] AND OLD RED SANDSTOKBl 488 

measures, and, on the East Lomond, with Moun? 
tain limestone.* 

Trap of the Old Red sandstone period, — By re- 
ferring to the section explanatory of the structure 
of Forfershire, already given (p. 99.), the reader 
will perceive that beds of conglomerate. No. 3.^ 
occur in the middle of the old red sandstone 
system, 1, 2, 3> 4. The pebbles in these conglo- 
merates are sometimes composed of granitic and 
quartz rocks, sometimes exclusively of diflFerent 
varieties of trap, which, although purposely omitted 
in the above section, are often found, either in«f 
truding themselves in amorphous masses and dikes 
into the older fossiliferous tilestones, No. 4., or 
alternating with them in conformable beds. All 
the different divisions of the red sandstone, 1, 2j 
3, 4, are occasionally intersected by dikes, but 
they are very rare in Nos. 1. and 2., the upper 
members of the group consisting of red shale and 
red sandstone. These phenomena, which occur at 
the foot of the Grampians, are repeated in the 
Sidlaw Hills ; and it appears that in this part of 
Scotland volcanic eruptions were most frequent in 
the earlier part of the old red sandstone period. 

The trap rocks alluded to consist chiefly of 
felspathic porphyry and amygdaloid, the kernels 
of the latter being sometimes calcareous, often 

* Fleming MS. Part of this tract I have myself ex- 
amined with Dr. F. 

Y 2 



484 SILURIAN VOLCANIC ROCKS. [Ptet IL 

ehalcedonic, and forming l>eautiful agates. We 
meet also with claystone, clinkstone, greenstone, 
compact felspar, and tuff. Some of these rocks 
flowed as lavas over the bottom of the sea, and 
enveloped quartz pebbles which were lying there, 
80 as to form conglomerates with a base of green- 
stone, as is seen in Lumley Den, in the Sidlaw 
Hills. On either side of the axis of this chain of 
hills (see section, p. 99.), the beds of massive 
trap, and the tuffs composed of volcanic sand and 
ashes, dip regularly to the south-east or north- 
west, conformably with the shales and sandstones. 

Dr. Fleming has observed similar trap rocks 
in the old red sandstone of northern Fifeshire, 
where they are covered immediately by the yel- 
low sandstone which forms the base of the moun- 
tain limestone and coal-measures. 

Silurian period. — It appears from the investiga- 
tions of Mr. Murchison in Shropshire, that when 
the lower Silurian strata of that county were ac- 
cumulating, there were frequent volcanic eruptions 
beneath the sea; and the ashes and scoriae then 
ejected gave rise to a peculiar kind of tufaceous 
sandstone or grit, dissimilar to the other rocks of 
the Silurian series, and only observable in places 
where syenitic and other trap rocks protrude.* 
These tuffs occur on the flanks of the Wrekin and 

* Murchison^ Silurian System, &c. p. 230. 



Ch. XXIILJ CAMBRIAN VOLCANIC BOCK& 435 

Caer Caradoe, and contain Silurian fossils, such as 
casts of encrinites, trilobites, and moUusca. Al- 
though fossiliferous, the stone resembles a sandy 
daystope of the trap family.* 

Thin layers of trap, only a few inches thick, 
alternate, in some parts of Slu*opsbire and Mont* 
gomerjrshire, with sedimentary strata of the lower 
Silurian system. This trap consists of slaty por- 
phyry and granular felspar rock, tlie beds being 
traversed by joints like those in the associated 
sandstone, limestone, and shale, and having the 
same strike and dip. f 

In Radnorshire, there is an example of twelve 
bands of stratified trap alternating with Silurian 
schists and flagstones in a thickness of 350 feet. 
The bedded traps consist of felspar-porphyry, 
clinkstone, and other varieties ; and the interposed 
Llandeilo flags are of sandstone and shale, with 
trilobites and graptolites. % 

Cambrian volcanic rocks. — In Pembrokeshire 
stratified greenstone, felspar-rock, and a brec- 
cia containing fragments of trap, alternate con- 
formably in thick parallel masses with regularly 
stratified sandstone and schist of the upper 
Cambrian system. These trappean masses, says 
Mr. Murchison, must have been evolved at in- 
tervals from volcanic fissures at the bottom of the 

* Murchison, Silurian System, &c. p. 230. 
t Ibid. p. 272. X Ibid. p. 325. 

Y 3 



48^ CAMBRIAN TOLCANIC ROCBBL tfutIL 

tea, wbai the sand, pebbles, and mud, now form- 
ing the accompanying sedimentary rocks, were 
deposited.* 

Professor Sedgwick, in his account of the geo^ 
kgy of Cumberland, has described various trap- 
rocks which accompany the green slates of the 
Cambrian system, beneath a limestone containing 
organic remains. Di£Perent felspathic and por- 
phyritic rocks and greenstones occur, not only in 
dikes, but in conformable beds; and there is occa« 
sionally a passage from these igneous rocks to some 
of the green quartzose slates. Professor Sedg- 
wick supposes these porphyries to have originated 
contemporaneously with the stratified chloritic 
slates, the materials of the slates having been sup- 
plied, in part at least, by submarine eruptions 
oftentimes repeated, f 

* Murchison, Silurian System, &c, p. 404. 
f Geol. Trans. 2d series, vol. iy. p. 55. 



487 



CHAPTER XXIV. 

ON THE DIFFERENT AGES OF THE PLUTONIC ROCKS. 

DilGiculty in ascertaining the precise age of a plutonic rock 
— Test of age by relative position — Test by intrusion 
and alteration — Test by mineral composition — Test by 
included fragments — Reccliit and Pliocene plutonic rocks, 
why invisible — Tertiary plutonic rocks in the Andes — ^ 
Granite altering Cretaceous rocks — Granite altering Lias 
in the Alps and in Sky — Granite of Dartmoor altering 
Carboniferous strata — Granite of the Old Red sandstone 
period — Syenite altering Silurian strata in Norway — , 
Blending of the same with gneiss — Most ancient plutonic 
rocks — Granite protruded in a solid form — On the pro- 
bable age of the granite of Arran^ in Scotland. 

When we adopt the igneous theory of granite, as 
explained in the 9th chapter, and believe that 
different plutonic rocks have originated at succes-*. 
sive periods beneath the surface of the planet, vre- 
must be prepared to encounter greater difficulty 
in ascertaining the precise age of such rocks, than 
in the case of volcanic and fossiliferous formations. 
We must bear in mind, that the evidence of the. 
age of each contemporaneous volcanic rock was de^ 
rived, either from lavas poured out upon the ancient 
surface, whether in the sea or in the atmosphere, 
or from tuffit and conglomerates, also deposited at 
the sur£EU^ and either containing organic remains 

Y 4 



488 TESTS OF RELATIVE AGE t^^ U* 

themselves, or intercalated between strata contain- 
ing fossils. But all these tests fail when we en- 
deavour to fix the chronology of a rock, which has 
crystallized from a state of fusion in the bowels of 
the earth* In that case, we are reduced to the 
following tests; 1st, relative position ; 2dly, intru- 
iSion, and alteration of the rocks in contact ; 3dly, 
mineral characters ; 4thly, included fragments. 

Test of age by relative position. — Unaltered fossil- 
iferous strata of every age are tnet with reposing 
immediately on plutonic rocks ; as at Christiania, in 
Norway, where the Newer Pliocene deposits rest 
on granite ; in Auvergne, where the freshwater 
Eocene strata, and at Heidelberg, on the Rhine, 
where the. New Red sandstone, occupy a similar 
place. In all these, and similar instances, inferior- 
ity in position is connected with the superior anti- 
quity of granite. The crystalline rock was solid 
before the sedimentary beds were superimposed, 
and the latter usually contain in them rounded 
pebbles of the subjacent granite. 

Test by intrusion and alteration. — But when 
plutonic rocks send veins into strata, and alter 
them near the point of contact, in the manner be- 
fore described (p. 204.), it is clear tfiat, like in- 
trusive traps, they are newer than the strata which 
they invade and alter. Examples of the appKea- 
tion of this test will be given in the sequel. 
. Test by mineral composition, — Notwithstanding a 



Ch. XXXV,1 , OF, PLUTOWC KOCK$.. ^^ 

general uniformity in the aspect of plutonie,rQck8| 
we have seen in the 9th chapter that there apjf 
Xnany varieties, such as Syenite, Talcose granit^i 
and. others. One of these varieties is sometime 
found exclusively prevailing throughout an extenr 
sive region, where it preserves a homogeneoug 
character; so that having ascertained its relative ag^ 
in one place, we can easily recognize its identity 
in others, and thus determine from a single seoticm 
the chronological relations of large mountain 
masses. Having observed, for example, that xhe 
syenitic granite of Norway, in which the mineral 
Called zircon abounds, has altered the Sihirian 
strata wherever it is in contact, we do not hesitate 
to refer all masses of the same zircon-syenite in 
the south of Norway to the same era. (See 
p. 242.) 

Some have imagined that the age of different 
granites might, to a great extent, be determined 
by their mineral characters alone; syenite, for 
instance, or granite with hornblende, being more 
modem than common or micaceous granite. JBut 
modem investigations have proved these gene^ 
ralizations to have been premature. The syenitic 
granite of Norway already alluded to may be of the 
same age as the Silurian strata, which it traverses 
and alters, or may belong to the Old Red saad;- 
stone period; whereas the granite of Dartmoor^ 

y 5 



490 BECENT AND FUOCXME [Tmt 11, 

(dthough consisting of mica, quartz, and felspar^ 
is newer than the CoaL (See p. 499.) 

Test by indudedJraffments.^^Tbi3 criterion can 
rarely be of much importance, because the frag- 
ments involved in granite are usually so much 
altered, that they cannot be referred with certainty 
to the rocks whence they were derived. In the 
White Mountains in North America, according to 
Professor Hubbard, a granite vein traversing gra- 
nite, contains fragments of slate and trap, which 
must have fallen into the fissure when the fused 
materials of the vein were injected from below*, 
and thus the granite is shown to be newer than 
certain superficial slaty and trappean formations. 

Recent and Pliocene plutonie rocks, why invisible. 
«?— The explanation already given in the 8th and 
9th chapters of the probable relation of the plu- 
tonie to the volcanic formations, will naturally lead 
the reader to infer, that rocks of the one class can 
never be produced at or near the surface without 
some members of the other being formed below 
simultaneously, or soon afterwards* It is not un- 
common for lava streams to require more than ten 
years to cool in the open air ; and where they are 
of great depth, a much longer period. The melted 
matter poured from Jorullo, iii Mexico, in the 
year 1 759, which accumulated in some places to 

* Silliman's Joiirn. No. 69. p. 123. 



ClkXXiy.] PLUTOMIC ROCKS. 491. 

the height of 550 feet, was found to retain a'bigb 
temperature half a century after the eruption.* 
We may conceive, therefore, that great masses of 
subterranean lava may remain in a red-hot or in^ 
candescent state in the volcanic foci for immense 
periods, and the process of refrigeration may be 
extremely gradual. Sometimes, indeed, this pro- 
cess may be retarded for an indefinite period, by 
the accession of fresh supplies of heat ; for we find 
that the lava in the crater of Stromboli, one of the 
Xapari islands, has been in a state of constant 
ebullition for the last two thousand years ; and we 
must suppose this fluid mass to communicate with 
some caldron or reservoir of fused matter below, 
lu the Isle of Bourbon, also, where there has been 
an emission of lava once in every two years for a 
IcMag period} the lava below can scarcely fail to 
h^ve been permanently in a state of liquefaction. 
If then it be a reasonable conjecture, that about 
2000 volcanic eruptions occur in the coiirse of 
every century, either above the waters of the sea 
or beneath themf, it will follow, that the quantitj^ 
of plutonic rock generated^ or in progress during 
the Recent epoch, must already have been con- 
siderable. 

But as the plutonic. rocks (originate at some 
depth in the earth's crust, they can only be rep- 

♦ See Principles, Index, " JoruUo." 
"I* Ibid. Index, ** Volcanic Eruptions." 

Y 6 



4&2 BBLATIVB AOB AND POSmOK ^-t^^^^ 

dered accessible to human observation J>jr siilne^ 
quent upbeaval and denudation. Between the 
period when a plutonic rock crystallizes in the 
subterranean r^ions, and the era of its protrusion 
at any single point of the surface, one or two 
geolc^ical periods must usually intervene. Hence, 
we must not expect to find the Recent or Newer 
Pliocene granites laid open to view, unless we ace 
prepsured to assume that sufficient time has elapsed 
since the commencement of the Newer Pliocene 
period for great upheaval and denudation. A 
l^utonic rock, therefore, must, in general, be of 
considei'able antiquity relatively to the fossiliferous 
and volcanic formations, before it becomes exten- 
sively visible. As we know that the upheaval of land 
has been sometimes accompanied in South America 
by volcanic eruptions and the emission of lava, we 
may conceive the more ancient plutonic rocks to 
be forced upwards to the surface by the newer 
rocks of the same class formed successively below, 
— subterposition in the plutonic, like superposi- 
tion in the sedimentary rocks, being usually cha- 
racteristic of a newer origin. 

In the accompanying diagram, Fig. 288., an at- 
tempt is made to show the inverted order in which 
sedimentary and plutonic formations may occur in 
the earth's crust. 



OF PLUTONIC R0CK9L 




494 TERTIARY PLUTONIC ROCKS tPartll 

The oldest plutonic rock, No. I., has been up- 
heaved at successive periods until it has become 
exposed to view in a mountain-chain. This pro- 
trusion of No. I. has been caused by the igneous 
agency which produced the new plutonic rocks 
Nos. II. III. and IV. Part of the primary fossil- 
iferous strata, No. 1., have also been raised to the 
surface by the same gradual process. It will be 
observed that the Recent strata No. 4., and the 
Recent granite or plutonic rock No. IV., are the 
most remote from each other in position, although 
of contemporaneous date. According to this hy- 
pothesis, the convulsions of many periods will be 
required before Recent granite will be upraised so 
as to form the highest ridges and central axes of 
mountain-chains. During that time the Recent 
strata No. 4. might be covered by a great many 
newer sedimentary formations. 

Tertiary plutonic rocks. — We have seen diat 
great upheaving movements have been experi- 
enced in the r^ion of the Andes, during the 
Recent and Newer Pliocene periods. In some 
part, therefore, of this chain, if any where, we may 
hope to discover tertiary plutonic rocks laid open 
to view. What we already know of die struc- 
ture of the Qiilian Andes seems to realize this 
expectation. In a transverse section, examined 

* 

by Mr. Darwio, between Valparaiso and Mendoza, 
the Cordillera was found to consist of two separate 



Cb, XZIV.] m THE ANDES. 495 

and parallel chains, formed of sedimentary rocks 
of different ages, the strata in both resting on plu^r^ 
tonic rocks, by which they have been altered. In 
the western or oldest range, called the Peuquenes, 
are black calcareous day-slates, rising to the 
height of nearly 14,000 feet above the sea, in 
which are shells of the genera Gryphaea, Turritella, 
Terebratula, and Ammonite. These rocks are sup- 
posed to be of the age of the central parts of the 
secondary series of Europe. They are penetrated 
and altered by dikes and mountain masses of a 
plutonic rock, which has the texture of ordinary 
granite, but rarely contains quartz, being a com- 
pound of albite and hornblende. 

The second or eastern chain consists chiefly of 
sandstones and conglomerates, of vast thickness^ 
the materials of which are derived from the ruins 
of the western chain. The pebbles of the con- 
glomerates are, for the most part, rounded frag- 
ments of the fossiliferous slates before mentioned 
The resemblance of the whole series to certain 
tertiary deposits on the shores of the Pacific, not 
only in mineral character, but in the imbedded 
lignite and silicified wood, leads to the conjecture 
that they also are teytiary. Yet these strata are 
not only associated with trap rocks and volcaniq 
tuffs, but are also altered by a granite newer than 
that of the western chain, and consisting of quartz, 
felspar, and talc They are traversed, moreover, 



4d6 l>LUTONIC BOCKS OF THE TFut IL 

by dikes of the same granite, and by nujiK^r<^i^ 
veins of iron, copper, arsenic, silver, and gQld;? 
all of which can be traced to the underlyipi^ 
granite.* We have, th^efore^ strong gix>im<i to 
presume that the plutonic rock, here exposed on, 
a large scale in the Chilian Andes, is of later ^^ 

than certain tertiary formations. 

Cretaceous period. — It was stated (p. 245.) that 

chalk as well as lias have been altered by granite 

in the eastern Pyrenees. Whether such granite 

be cretaceous or tertiary cannot easily be decided. 

Fig. 289. Suppose &, c, c^ to be 

three members of the 
Cretaceous series, the 
lowest of which, h^ has 
been altered by the 
granite A, the modifying 
influence not having extended so fer as c, or 
having but slightly afiPected its lowest beds. Now 
it can rarely be possible for the geologist to decide 
whether the beds d existed at the time of the in- 
trusion of A, and alteration of h ahd c, or whether 
they were subsequently thrown down upon c. 

As some Cretaceous rocks, however, have been 
raised to the height of more than 9000 feet in 
the Pyrenees, we must not assume diat plutonie 
formations of the same age may not have been 

* Darwin, pp. 390. 406. 




Ck.XXIV.] CHALK, OOLITE, AND LIAS. 497 

brought up &nd exposed by denudation, at die 
height of 2000 or 3000 feet on the flanks of that 
ch^. 

Period ^ Ooliie and Lias. — In the department 
of the Hautes Alpes, in France, near Vizille, M. 
Elie de Beaumont traced a black ai^llaceous 
limestone, charged with belemnites, to within a few 
yards of a mass of granite. Here the limestone 

Fig. 290. 




JlowtiiM tfgranUC allli Jaraule or OaUli 



hegias to put on a granular texture, but is ex- 
tremely fine-^^ined. When nearer the junction 
it becomes grey, and has a saccharoid structure. 
In another locality, near Champoleon, a granite 
composed of quartz, black mica, and rose-coloured 
felspar, is observed partly to overlie the secondary 
rocks, producing an alteration which extends for 



49& TRAP ROCKS COEVAL WITff C VMt II. 

about thirty feet downwards, diminishing in the 
beds which lie farthest from the granite. (See 
Fig. 290.) In the altered mass the argillaceous 
beds are hardened, the limestone is saccharoid, 
the grits quartzose, and in the midst of them is a 
thin layer of an imperfect granite. It is also an 
important circumstance, that near the point of 
contact, both the granite and the secondary rocks, 
become metalliferous, and contain nests and small 
veins of blende, galena, iron, and copper pyrites. 
The stratified rocks become harder and more 
crystalline, but the graiiite, on the contrary, softer 
and less perfectly crystallized near the junction.* 

Although the granite is incumbent in the above 
section (Fig. 290.), we cannot assume that it over- 
flowed the strata, for the disturbances of the rocks 
are so great in this part of the Alps that they sel- 
dom retain the position which they must originally 
have occupied. 

A considerable mass of syenite, in the Isle of Sky, 
is described by Dr. MacCulloch as intersecting 
limestone and shale, which are of the age of the 
lias, f The limestone, which, at a greater distance 
from the granite, contains shells, exhibits no traces 

* Etie de Beaumckot, sur les Montagnes dis l'Oisans> &c.» 
M^.de laSoc. d'Hist. Nat. de Paris, tome v. 

f See Murchison, Geol. Trans., 2nd series, voL ii.'part iL 
pp.311 — ^321. 



Ck.XXtV.2 OOLITE AND COAX. 490 

bf them near its junction, where it has been con- 
verted into a pure crystalline marble.* 

At Predazzo, in the Tyrol, secondary strata, 
some of which are limestones of the Oolitic period, 
have been traversed and altered by plutonic rocks, 
one portion of which is an augitic porphyry, which 
passes insensibly into granite. The limestone is 
changed into granular marble, with a band of ser- 
pentine at the junction, f 

Carbanifirotis period. — The granite of Dart- 
moor, in Devonshire, was formerly supposed to be 
one of the most ancient of the plutonic rocks, but 
is now ascertained to be posterior in date to the 
culm-measures of that county, which, from their 
position, and as containing true coal-plants, are 
regarded by Professor Sedgwick and Mr. Mur- 
chison as members of the true carboniferous 
series. This granite, like the syenitic granite of 
Christiania, has broken through the stratified 
formations without much changing their strike. 
Hence, on the north-west side of Dartmoor, the 
successive members of the culm-measures abut 
against the granite, and become metamorphic as 
they approach. These strata are also penetrated by 
granite veins and plutonic dikes, called '^elvans.'':|: 



* Western Islands, vol. i. p. 330. plate 18. figs. 3, 4. 

f Von Buch, Annates de Chimie, &c. 

j* Proceedings of Geol. Soc., vol. IL p. 562. 



500 GHANHC OF OLD RED IPatill. 

The granite of Cornwall is probably of the same 
date, and, therefore^ as modem as the Carbonifer- 
ous strata, if not much newer. 

Oid Red sandafyme period. — The plutonic rocks 
of the Malvern hills, in Worcestershire, consist of 
a granitic compound of quartz, felspar, and horn- 
blende, or occasionidly of quartz, mica, and fel- 
spar, which passes into syenite and greenstone.* 
This rock has altered the adjacent Silurian strata 
into well characterized metamorphic schists, prin- 
cipally chloritic and micaceous-schist, with some 
gneiss, and has dislocated and reversed the posi- 
tion of the beds of the Silurian and Old Red 
sandstone. There are indications, says Mr. Mur- 
chison, of several periods of movement, by which 
the strata were forced up and folded back, but the 
chief outburst was after tlie accumulation of the 
Silurian and part of the Old Red system, and 
anterior to the formation of the coal-beds, which 
are undisturbed* f 

• Siberian period* — I have already alluded to the 
granite near Christiania, in Norway, as being 
2iewer than the Silurian strata of that r^on. 
Its posteriority in date to limestones containing 
orthocerata and trilobites, has long been cele- 
brated, it being twenty-five years since Von Buch 
first announced the discovery. The proofs consist 

• Mr. L. Horner, Geol. Trans., 1st ser., vol. i. p. 281. 
+ SiluritUi System, p. 425. 



Cb,XXlV.2 AND SILURIAN PERIODS. 50] 

in the penetration of granite veins into the shale 
and limestone, and the alteration of the strata, &r 
a considerable distance from the point of contact, 
both of these veins and the central mass from 
which they emanate. (See p. 215.) Von Bueh 
supposed that the plutonic rock alternated with 
the fossiliferous strata, and that large masses of 
granite were sometimes incumbent upon the strata; 
but this idea was erroneous, and arose from the 
fact that the beds of shale and limestone often dip 
towards the granite up to the point of contact, 
appearing as if they would pass under it in mass, 
as at a, Fig. 291., and then again on the opposite 
side of the same mountain, as at by dip away from 
the same granite. When the junctions, however. 

Fig. 29L 




Silurian. Granite. Silurian strata. 

are carefully examined, it is found that the plu- 
tonic rock intrudes itself in veins, and no where 
covers the fossiliferous strata in large overlykig 
masses, as is so commonly the case with trappean 
formations.* 

Now this granite, which is more modem than 

* See the G»a Norvegica and other works of KeilhaOy 
with whom I examined this country. 



502 GRANITE ALTEBINa ITvci IL 

the Silurian stxata of Norway, also sends veins in 
the same country into an ancient formation of 
gneiss ; and the relations of the plutonic rock and 
the gneiss, at their junction, are full of interest 
when we duly consider the wide difference of 
epoch which must have separated their origin* 

The length of this interval of time is attested 
by the following &cts : — The fossiliferous, or 
transition beds, rest unconformably upon the 
truncated edges of the gneiss, the inclined strata 
of which had been disturbed and denuded be- 
fore the sedimentary beds were superimposed. 
(See Fig. 292,) 

Fig. 292. 




Gneiss. Granite. Gneiss. 

Granite tending veins inlo Silurian strata and Gneiss, — Christiania, Norway, 

The signs of denudation are twofold; first, the 
sur&ce of the gneiss is seen occasionally on the 
removal of the newer beds, containing organic 
remains, to be scored and polished; secondly, 
pebbles of gneiss have been found in some of the 
transition strata. Between the Origin, therefore, 
of the gneiss and the granite there intervened, 
jSrst, the period when the strata of gneiss were 
inclined; secondly, the period when they were 



SUh. XXIV.] SILURIAN STRATA. 503 

denuded; thirdly, the period of the deposition of 
the transition deposits. Yet the granite produced, 
after this long interval, is often so intimately blended 
^th the ancient gneiss, at the point of junction, 
that it is impossible to draw any other than an 
arbitrary line of separation between them; and 
where this is not the case, tortuous veins of gra- 
nite pass freely through gneiss, ending sometimes 
in threads, as if the older rock had offered no re* 
sistance to their passage. It seems necessary, 
therefore, to conceive that the gneiss was softened 
and more or less melted when penetrated by the 
•granite. But had such junctions alone been visi- 
ble, and had we not learnt, from other sections, 
how long a period elapsed between the consolida- 
tion of the gneiss and the injection of this granite, 
we might have suspected that the gneiss was 
scarcely solidified, or had not yet assumed its com- 
plete metamorphic character, when invaded by 
the plutonic rock. From this example we may 
learn how impossible it is to conjecture whether 
certain granites in Scotland, and other countries, 
which send veins into gneiss and other metamor- 
phic rocks, are primary, or whether they may not 
belong to some secondary or tertiary period. 

Jilost ancient granites, — It is not half a century 
since the doctrine was very general that all granitic 
rocks were primitive^ that is to say, that they ori- 
ginated before the deposition of the first sedimen- 



504 V08T ANCIEHT GBAKITBS. ' t^Ut IL 

tary strata, and before die creation of organic 
beings. (Seep. dO.) But so great! j are bur viewg 
now changed, that we find it no easy task to point 
out a single mass of granite demonstrably more 
ancient than all the known fossiliierousclepotitti 
Could we discover some Lower Cambrian strata 
resting immediately on granite, there being no 
alterations at the point of contact, nor any inter- 
secting granitic veins, we might then dffirm> the 
plutonie rock to have originated before the oldest 
known fossiliferous strata. Still it would be pre** 
sumptuous to suppose that when a small part onlj 
of the globe has been investigated, we are ac- 
quainted with the oldest fossiliferous strata in the 
crust of our planet Even when these are found, 
we cannot assume that there never were any ante- 
cedent strata containing organic reoiains, which may 
have become metamorphic If we find pebbles of 
granite in a conglomerate of the Lower Cambrian 
system, we may then feel assured that the parent 
granite was formed before the Lower Cambrian 
formation. But if the incumbent strata be merely 
Silurian or Upper Cambrian, the fundamental 
granite, although of high antiquity, may be posta- 
rior in date to knaum fossiliferous formations* 

Pfotrtisian of solid ffranite. — In part of Suther- 
landshire, near Brora, common granite, composed 
of felspar, quartz, and mica, is in immediate contact 
with Oolitic strata, and has clearly been elevated to 



Cb. XX{V.] PROTRUSION OF SOLID GRANITE. 505 

tbfe sur&ce at a period subsequent to the depositioa 
of those strata. *" Professor Sedgwick and Mr« 
Murchison. conceive that this granite h^ been 
upheaved in a solid form ; and that in breaking 
tlyrough the submarine deposits, with which it was 
not perhaps originally in contact, it has fractured 
them so as to form a breccia along the line of 
junction* This breccia consists of fragments of 
shale, sandstone, and limestone, with fossils of the 
oolite^ all united together by a calcareous cemenu 
The secondary strata, at some distance from the 
graiiiite, are but slightly disturbed, but in propor^ 
tion to their proximity the amount of dialocation 
becomes greater* 

If we admit that solid hjrpogene rocks, whether 
stratified Qr unstratified, have in such casea been 
driven upwards so as to pierce through yielding 
sedimentary deposits, we shall be enabled to 
account for many geological appearances otherwise 
inexplicable. Thus, for example, at Weinbbhla 
and Hohnstein, near Meissen, in Saxony, a mass 
of granite has been observed covering strata of the 
cretaceous and oolitic periods for the ^ace of be* 
tween 300 and 400 yards square. It appears 
clearly fix)m a recent memoir of Dr. B, Cotta on 
this subject f, that the granite was thrust into its 

* Murchison, Geol. Trans. 2d series, vol.ii. p. 307. 
f Geogno8t38che Wandemngen, Leipzig, 1838. 

Z 



506 A.GK OF THE 6BANITB [Fan It. 

actual position when solid. There are no inter- 
secting veins at the junction — no alteration as if 
by heat, but evident signs of rubbing, and a brec- 
cia in some places, in which pieces of granite are 
mingled with broken fragments of the secondary 
rocks. As the granite overhangs both the lias and 
chalk, so the lias is in some places bent over strata 
of the cretaceous era. 

jlge of the granite ofArraiu — In this island, die 
largest in the Firth of Clyde, on the west coast of 
Scotland, the four great classes of rocks, the fossi- 
liferous, volcanic, plutonic, and metamorphic, are 
all conspicuously displayed within a very small 
area, and with their peculiar characters strongly 
contrasted. In the north of the island the granite 
vised to the height of nearly 3000 feet above die 
sea, terminating in mountainous peaks. On the 
flanks of the same mountains are chloriticHschists, 
blue roofing<^slate, and other rocks of the meta- 
morphic order (a), into which the granite (b) 
sends veins. These schists are highly inclined. 
On their truncated edges rest unconformable beds 
of conglomerate and sandstone, to which succeed 
various shales and limestones, containing fossils of 
the carboniferous period. All these secondary 
strata (c) are much tilted and inclined near the 
hypogene rocks; but are horizontal at a distance 
from them, as in the south of Arran. Lastly, the 
volcanic rocks (d), consisting of greenstone, pitch- 



Gh. XXtV.] 



OF THE 1SLB OF AARAK. 



507 



Fig. 293. 



Section of Airan. 




d 

A, Crystalline, or metamorphic schist. b, Granite. 

c. Conglomerate, sandstone, limestone, and shale. d, Trap. 



Stone, claystone, porphyry, and other varieties, 
traverse all the preceding formaticms, cutting 
through the granite in dikes {d)^ as well as through 
the sandstone; which last they also overlie in 
dense masses, from 50 to 700 feet in thickness* 

Now as the diiSerent kinds of trap intersect all 
the other formations, they are certainly the newest 
rocks in Arran. The red sandstone and other 
secondary strata are older than the trap, but newer 
than the metamorphic schists, for the Red sand- 
stone conglomerates not only rest unconform- 
ably upon the schists, but contain rounded pebbles 
of those crystalline strata. It is equally certain 
that the schists are the oldest rocks in the island :. 
they are more ancient than the trap and red 
sandstone, for reasons already stated; and the 
granite must be of new^ origin, because it pene- 
trates them in veins* The only chronological 
point, therefore, in which there can be any am- 
biguity, relates to the plutonic formations. They 

z 2 



fi08. AOE OF. THE ORAKITEr (Fttt U. 

are more modem, as before remarked, than the 
crystaUine schists ; but can we decide them to be 
likewise yomiger than the secondary sandstones? 
Now it is a curious and most striking fact, that 
no pebbles of granite have ever been found in the 
conglomerates of the red sandstone in Arraoy 
although careful search has been made for them 
by many geologists; »nd althoi^h puddingstones 
in general are chiefly made up of fragments of 
older rocks of the immediate vicinity. The total 
absence of such pebbles has justly been a theme 
of wonder to those who have visited Arran, and 
have seen that the conglomerates are several 
hundred feet in thickness, and that they occur at 
the base of the granite mountains, which tower 
above them in far bolder and more picturesque 
forms than those of similar composition in other 
parts of Scotland. We may at once infer, with 
confidence, that when the sandstone and conglo' 
merate were formed, no granite had reached the 
surface, or had been exposed to denudation in this- 
region : the crystalline schists were ground into 
sand and shingle when these puddingstones were 
accumulated, but the waves had never acted- upon 
the granite, wMch sends its veins into the schist 
Are we then to conclude, that the schists suffered 
denudation before- they had been invaded by 
granite? This opinion, although it cannot be 
disproved, is by no means fully borne out by the 



<ni. XXIV.] .OF THE ISLE OF ARfiAN. (S09 

-evideiKie. At the time when the fed sandstone 
was formed^ the metamorphic strata may have 
formed islands in the sea,, as in Fig. 294., over which 
,the breakers rolled, or from which torrents and 
rivers descended, carrying down gravel and sand. 
The plutonic rock (b) may have been previously 

Fig. 294. 
Sea 




injected at a certain depth below, and yet may 
never have been exposed to denudation. 

As to the time and manner of the subsequent 
protrusion of the hypogene rocks in Arran, these 
are questions into which I have not space to enter 
at present : I shall merely observe, that those crys- 
talline rocks may have been thrust up bodily, in a 
solid form ; and it is clear that, during or since 
the period of their emergence, they have under- 
gone great aqueous denudation. This action is 
confirmed by three distinct kinds of proofs: 1st, 
The occurrence of scattered pebbles and huge er- 
ratic blocks of granite and schist over the surface 
of Arran and the adjacent mainland ; 2dly, The 
abrupt truncation of dikes, such as those at d 
(Fig. 293.), cut off on the surface of the granite ; 
3dly, The fact, that not only the secondary 
strata but the enormous masses of trap which ac- 

z 3 



510 ' ORAKITB OF ARRAK [Put it 

company and overlie them, terminate suddenly on 
reaching the borders of the granite and schist, 
towards which they often present a steep escarp- 
ment, and over which, for some distance at least, 
they must originally have extended.* 

• 

* In the works of Drs. Hutton and MacCuUoch, and in 
the Memoirs of Messrs. Yon Dechen and Oeynhausen, and 
that of Professor Sedgwick and Mr.Murchison (Geol. Trans. 
2d series) and others, whose observations I have verified 
on the ]qK>t, the reader will find a fuU description of the 
geology of Arran. 



511 



CHAPTER XXV. 

on THE DIFFERENT AGES OF THE METAMORPHIG ROCKS. 

Age of each set of metamorphic strata twofold — Test of 
age by fossils and mineral character not available — Test 
by superposition ambiguous — Conversion of dense masses 
of fossiiiferous strata into metamorphic rocks — Lime* 
stone and shale of Carrara — Metamorphic strata of mo- 
dern periods in the Alps of Switzerland and Savoy — 
Why the visible crystalline strata are none of them very 
modem — Order of succession in metamorphic rocks — 
Uniformity of mineral character — Why the metamorphic 
strata are less calcareous than the fossiiiferous. 

r 

According to the theory adopted in the 11th 
chapter, the age of each set of metamorphic strata 
is twofold, they have been deposited at one period, 
they have become crystalline at another. We 
can rarely hope to define with exactness the date 
of both these periods, the fossils having been de- 
istroyed by plutonic action, and the mineral charac- 
ters being the same, whatever the age. Superposi- 
tion itself is an ambiguous test, especially when we 
desire to determine the period of crystallization. 
Suppose, for example, we are convinced that ceri- 
tain metamorphic strata in the Alps, which are 
covered by cretaceous beds, are altered lias; this 
lias may have assumed its crystalline texture in 
the cretaceous or in some tertiary period, the 

z 4 



512 AGE OF METAMORPHIC ROCKS tPutU. 

Eocene for example. If in the latter, it should 
be called Eocene^ \7hen regarded as a meta^ 
morphic rock, although it be liassic, when consi-^ 
dered in reference to the era of its deposition. 
According to this view, the superposition 6f chalk 
does not prevent the subjacent metamarphic rock 
from being Eocene. Ifi however, in the progress 
of science, we should succeed in ascertaining the 
twofold chronological relations of the metamorphic 
formations, it might be useful to adopt a twofold 
terminology. We might call the strata above al- 
luded to Liassic-Eocene, or Liassic-Cretaceous ; 
the first term referring to the era of depositipn, 
the second to that of crystallization. According 
to this method, the chlorite-schist, mica-schist, and 
gneiss of the Malvern Hills, would belong to the 
Silurian -Old Red sandstone period, because they 
are Silurian strata altered into metamorphic 
rocks during the deposition of the Old Red sand? 
stone. (See p. 500.) 

We have seen, when discussing the ages of the 
plutonic rocks, that examples occur of various pri- 
mary, secondary, and tertiary deposits converted 
into metamorphic strata, near their contact with 
granite. There can be no doubt in these cases 
that strata, oiice composed of mud, sand, and 
^gravel, or of clay, marl, and shelly limestone^ 
Jbave for the distance of several yards, and in some 
instances several hundred feet, been turned intg 



.Ch. XX;V.] OF THE NORTHERN AFENNINEa ^13 

^eiss, mica-schist, homblende-schist^ chlorite- 
■schist, quartz rock, statuary marble, and the rest* 
-(See Chapters 10. and 11.) 

But when the metamorphic action has operated 
on a grander scale, it tends entirely to destroy all 
monuments of the date of its development It 
may be easy to prove the identity of two different 
parts of the same stratum ; one, where the rock 
has been in contact with a volcanic or plutonic 
jnass, and has been changed into marble or horn*- 
blende-schist, and another not far distant, where 
the same bed rem^ains unaltered and fossiliferous ; 
but when we have to compare two portions of a 
mountain chain — the one metamorphic, and the 
^ther unaltered — all the labour and skill of the 
'most practised observers are required, I shall 
-mention one or two examples of alteration on a 
grand scale, in order to explain to the student the 
kind of reasoning by which we are led to infer that 
dense masses of fossiliferous strata have been con- 
verted into crystalline Tocks. 

Northern Apennines. — Carrarcu — The celebrated 
marble of Carrara, used in sculpture, was once 
regarded as a type of primitive limestone. It 
abounds in the mountains of Massa Carrara, or 
the " Apuan Alps," as they have been called, th^ 
highest peaks of which are nearly 6000 feet high. 
Its great antiquity was inferred from its mineral 
•texture, from the absence of fossils, and its passage 

z 6 



514 AGE OF HETAMOftPRlC BOCK8 I tF«tIL 

downwards into talc-schist and gametiferoiis nuca« 
schist; diese rocks again graduating downwards 
into gneiss, which is penetrated, at Fomo, by gra* 
nite veins. Now the researdies of MM. Savi, 
Boue, Pareto, Guidoni, De la Beche, and^especi- 
ally Hoffinann, have demonstrated that this marble, 
once suposed to be formed before the existence of 
organic beings, is, in fact, an altered limestone of 
the oolitic period, and the underlying crystalline 
schists are secondary sandstones and shales, mo- 
dified by plutonic action. In order to establish 
these conclusions it was first pointed out, that the 
calcareous rocks bordering the Gulf of Spezia, and 
abounding in oolitic fossils, assume a texture like 
that of Carrara marble, in proportion as they are 
more and more invaded by certain trappean and 
plutonic rocks, such as diorite, euphotide, serp^it* 
ine, and granite, occurring in the same country. 

It was then observed that, in places where the 
secondary formations are unaltered, the uppermost 
consist of common Apennine limestone with no- 
dules of flint, below which are shales, and at die 
base of all, argillaceous and siliceous sandstones. 
In die limestone, fossils are frequent, but veiy 
rare in the underlying shale and sandstone. Now 
a gradation has been traced laterally from these 
rocks into another and corresponding series, which 
is completely metamorphic ; for at the top of this 
we find a white granular marble, whoDy devoid of 



Ch. XXV.] OF THE SWISS ALPS 516 

fossils, and almost without stratification, in which 
there are no nodules of flint, but in its place sili*- 
ceous matter disseminated through the mass in 
the form of prisms of quartz. Below this, and 
in place of the shales, are talc-schists, jasper, and 
hornstone; and at the bottom, instead of the sili- 
ceous and argillaceous sandstones, are quartzite 
and gneiss.* Had these secondary strata of the 
Apennines undergone universally as great an 
amount of transmutation, it would have been im- 
possible to form a conjecture respecting their 
true age; and then, according to the common 
method of geological classification, they would, 
have ranked as primary rocks. In that case the 
date of their origin would have been thrown back 
to an era antecedent to the deposition of the 
Lower Cambrian strata, although in reality they 
were formed in tlie oolitic period, and altered at 
some subsequent and unknown epoch. 

Alps of Stvitzerland. — In the Alps, analogous 
eondusions have been drawn respecting the alter- 
ation of strata on a still more extended scale* 
In the eastern part of that chain, some of the pri- 
mary fossiliferous strata, as well as the older 
secondary formations, together with the oolitic and 
eretaceous rocks, are distinctly recognizable. Ter- 

* See Notices of Savi, Hoffmann, and others, referred to 
by Boue, Bull, de la Soc. Geol. de France, torn. y. p. 317 
and torn. iii. p.xliv. . 

z 6 



filS AGE QF HBTAMQRPHIC HOCKS [P^rt II« 

tiary deposits also appear in a less elevated posir 
^on on the flanks of the Eastern Alps ; but in the 
Central or Swiss Alps, the primary fossiliferousi 
and older secondary formations disappear, and 
the cretaceous, oolitic, and liassic strata gra« 
duate insensibly into metamorphic rocks, consist* 
ing of granular limestQne, talc-schist, talcose^ 
gneiss, micaceous schist, and other varieties. Ia 
regard to the age of this vast assemblage of crys- 
talline strata, we can merely affirm that some of 
the upper portions are altered newer secondary 
deposits : but we cannot avoid suspecting that the 
disappearance both of the older secondary and 
primary fossiliferous rocks may be owing to their 
having been all converted in this region into crys« 
talline schist 

It is difficult to convey to those who have never 
visited the Alps a just idea of the various proofe 
which concur to produce this conviction. In the 
first place, there are certain points where strata of 
the Oolite, Lias, and Chalk have been turned into, 
granular marble, gneiss, and other metamorphic 
schists, near their contact with granite. This fact 
shows undeniably that plutonic causes continued 
to be in operation in the Alps down to a late pe- 
riod, even after the deposition of some of th^ 
newer secondary formations. Having established 
this point, we are the more willing to believe that 
many Inferior fossiliferous rocks, probably exposed 



Ch.XXV.] OF THE SWISS ALPS. fil7 

for longer pieriods to a similar action, may have 
'become metamorphic to a still greater extent* 

We also discover in parts of the Swiss Alps dense 
masses of strata of the age of the Green-sand and 
Chalk, which have assvimed that semi-crystalline 
texture which Werner called transition, and which 
naturally led his followers, who attached great im^ 
portanceto mineral characters taken alone, to class 
them as transition formations, or as groups older 
Ithan the lowest secondary rocks. (See p. 263.) 
Now, it is probable that these strata have been 
affected, although in a less intense degree, by tha( 
same plutonic action which has entirely altered 
and Tendered metamorphic so many of the subja^ 
cent formations ; for in the Alps, this action has 
by no means been confined to the immediate vici-^ 
nity of granite. Granite, indeed, and other plu-» 
tonic rocks rarely make their appearance at the 
surface, notwithstanding the deep ravines whiclii 
lay open to view the internal structure of these, 
mountains. That they exist below at tio great 
depth we cannot doubt, and we have already seen, 
(p. 211.) that at some points, as in the Valorsine^ 
near Mont Blanc, granite and granitic Veins are. 
observable, piercing through talcose gneiss, which 
passes insensibly upwards into secondary strata. 

It is certainly in the Alps of Switzerland and 
Savoy, more than in any other district in Europe^ 
that the geologist is prepared to meet with jthe signa^ 



B18 AOE OF XETAKOBPHIC R0CK8 . IPkTtIt 

of an intense development of plntonic action ; fiir 
here we find the most stupendous monuments of 
mechanical violence^ by which strata thousands of 
feet thick have been bent, folded, and overturned 
{See p. 113.) It is here that marine secondary 
formations of a comparatively modem date, such 
as the oolitic and cretaceous, have been upheaved 
to the height of 10,000, or even 12,000 feet above 
the level of the sea ; and even tertiary strata, ap* 
parentiy of tiie Miocene era, have been raised to 
an elevation of 4000 or 5000 feet, so as to rival in 
height the loftiest mountains in Great Britain. 

If the reader will consult the works of many 
eminent geologists who have explored the Alps, 
especially those of MM. De Beaumont, Studer, 
Necker, and Bou^, he will learn that they all share, 
more or less fully, in the opinions above expressed. 
It has, indeed, been stated by MM. Studer and 
Hugi, that there are complete alternations on a 
large scale of secondary strata, containing fossils, 
with gneiss and other rocks, of a perfectiy meta- 
morphic structure. I have visited some of the 
most remarkable localities referred to by these 
authors, but although agreeing with tiiem that 
there are passages from the fossiliferous to llie 
metamorphic series far from tlie contact of granite 
or other plutonic rocks, I was unable to convince 
myself tiiat the distinct alternations of highly crys- 
talline^ with unaltered strata above alluded to^ 



Ch. XXV.] OF THE SWISS ALPS. .. 519 

might not admit of a different explanation. In 
one of the sections described by M. Studer in the 
highest of the Bernese Alps, namely in the Roth- 
thai, a valley bordering the line of perpetual snow 
on the northern side of the Jungfrau, I observed 
a mass of gneiss 1000 feet thick, and 15,000 feet 
long, not only restuig upon, but also again covered 
by strata containing oolitic fossils. These anoma- 
lous appearances may partly be explained by sup- 
posing great solid wedges of intrusive gneiss to 
have been forced in laterally between strata to 
which I found them to be in many sections un- 
conformable. The superposition, also, of the 
gneiss to the oolite may, in some cases, be due 
to a reversal of the original position of the beds in 
a region where the convulsions have been on so 
stupendous a scale. 

On the Sattel also, at the base of the Ges- 
tellihorn, above Enzen, in the valley of Urbach, 
near Meyringen, some of the intercalations of 
gneiss between fossiliferous strata may, I conceive, 
be ascribed to mechanical derangement. Almost 
any hypothesis of repeated changes of position 
may be resorted to in a region of such extraordi- 
nary confusion. The secondary strata may first 
have been vertical, and then certain portions may 
have become metamorphic (the plutonic influence 
ascending from below) while intervening strata 
remained unchanged. The whole ^series of beds 



SSM) AGE OF METAKORPHIC ROCKS, ' tP^It 

anay then again have been thrown into a 
'nearly horizontal position, giving rise to the su*- 
•perposition of crystalline upon fossiliferous form^ 
litions. 

It was remarked, in the last chapter, that as the 
hypogene rocks, both stratified and unstratified, 
crystallize originally at a certain depth beneath 
the surface, they must always, before they are up- 
raised and exposed at the surface, be of consider^ 
fitble antiquity, relatively to a large portion of the 
fossiliferous and volcanic rocks. They may be 
forming at all periods ; but before any of them 
ican become visible, they must be raised above 
the level of the sea, and some of the rocks which 
previously concealed them must have been re- 
moved by denudation. If the student will refer 
to the frontispiece, he will see that the strata A, 
which were the last deposited, are every where 
hidden from human observation by the sea, while 
the contemporaneous metamorphic rocks C are 
concealed at a still greater depth, as are also the 
plutonic rocks D of the same age. He will also 
observe that the strata C, which have recently 
become metamorphic, are not parts of A, nor 
even of the groups immediately antecedent in 
date (0, i, c, but they are portions of much older 
formations, d, e^f, g^ A, z. Now, suppose that part 
of the earth-s crust, which is represented in the 
irpntispiece to be subjected, in various places, tQ 



, tau XXV.] AND ORDER DF SUPERPOSITION. $2 1 

.a long series of upheaving and depressing move* 
ments; the beds A will, here and there, be par- 
tially upraised and converted into dry land) but 
vthe hjrpogene rocks C, D, although brought lip 
.nearer to the surface,. will still, very probably, re- 
main hidden from sight Let a second period 
elapse and the rocks A may be raised in some 
countries to a height of several thousand feet; and 
still the rocks C and D may be almost every 
where hidden. During a third period, when the 
stratified formations A have been laid dry over 
large continental areas, and have reached the sum* 
jnits of some Alpine chains, the hypogene forma- 
. tions C D may also be forced up and exposed to view 
above the level of the ocean by similar causes ; 
but they will rank no longer as modemjocks, the 
geologist being already acquainted with newer 
groups, both fossiliferous and volcanic. The stu- 
dent will also perceive how impossible it may then 
be to prove that the strata C became metamorphic 
at the period of the deposition of A, and how diffi- 
cult jiot to exaggerate the antiquity of C as a series 
of metamorphic rocks, when the remote period of 
their deposition has been ascertained, and the 
comparatively modern era of their crystallization 
remains uncertain. 

Order of succession in Metamorphic rocks, — - 

There is no universal and invariable order of 

,3uperpo$ition in metamorphic rocks, although a 



522 CSBONOLOGICAL BSLATIONS tPutH. 

parUcular arrangement may prevail throughout 
<x>untrie8 of great extent, for the same reason that 
it is traceahle in those sedimentary formations 
from which crystalline strata are derived. Thus, 
for example, we have seen that in the Apennines, 
near Carrara, the descending series, where it is 
metamorphic, consists o^ 1st, saccharine marble; 
2dly, talcose^schist ; and 3dly, of quartz-rock and 
gneiss; where unaltered, of, 1st, fossiliferous lime- 
stone; 2dly, shale; and ddly, sandstone. 

But if we investigate different mountain chains 
we find gneiss, mica-schist, homblende-schist, 
chlorite-^chist, hypogene limestone, and other 
rocks, succeeding each other, and alternating with 
each other, in every possible order. It is, indeed, 
more common to meet with some variety of clay- 
'slate forming the uppermost member of a meta- 
morphic series than any other rock ; but this &ct 
by no means implies, as some have imagined, that 
all clay-slates were formed at the close of an ima* 
ginary period, when the deposition of the crystal- 
line strata gave way to that of ordinary sedimentary 
deposits. Such clay-slates, in fact, are variable in 
composition, and sometimes alternate with fossili- 
ferous strata, so that they may be said to belong 
almost equally to the sedimentary and metamor* 
phic order of rocks. It is probable that had they 
been subjected to more intense plutonic action, 
they would have been transformed into hon>- 



.Ch. XXVJ OF METAMORPHIC ROCK& 525 

blende-schist, foliated chlorite-schist, scaly talcose^ 
schist, mica-schist, or other more perfectly crys^ 
talline rocks, such as are usually associated with 
gneiss. 

Uniformity of mineral character in Hypogene 
rocks, — Humboldt has emphatically remarked that 
when we pass to another hemisphere, we see new 
forms of animals and plants, and even new con* 
stellations in the heavens ; but in the rocks we 
still recognize our old acquaintances, — the same 
granite, the same gneiss, the same micaceous schist^ 
quartz-rock, and the rest It is certainly true that 
there is a great and striking general resemblance 
in the principal kinds of hypogene rocks, although 
of very different ages and countries ; but it has 
been «hown that each of these are, in fact, geolo- 
gical families of rocks, and not definite mineral 
compounds. They are much more uniform in 
aspect than sedimentary strata, because these last 
are often composed of fragments varying greatly in 
form, size, and colour, and contain fossils of differ- 
ent shapes and mineral composition, and acquire 
a variety of tints from the mixture of various 
kinds of sediment. The materials of such strata^ 
if melted and made to crystallize, would be sub^ 
ject to chemical laws, simple and uniform in their 
action, the same in every climate, and wholly un* 
disturbed by mechanical and organic causes. 



;S24 HYPOGENE ROCKS. ' C.^Pirtll. 

N^veriheless, it would be & great erroi^ to assuisie 
4liat the hypogene rocks, considered as aggregates 
of simple minerals, are really more homogeneous 
in their composition than the several members of 
•the sedimentary series. In the first plaice, different 
.leussemblages of hypogene rocks occur in different 
tK>untries; and secondly, in any one district, die 
jrocks which pass imder the same name are often 
extremely variable in their component ingredients, 
or at least in the proportions in which each of these 
fire present. Thus, for example} gneiss and mica* 
schist, so abundant in the Grampians, are wanting 
in Cumberland, Wales, and Cornwall ; in parts of 
the Swiss and Italian Alps, the gneiss and granite 
are talcose, and not micaceous, as in Scotland; horn* 
blende prevails in the granite of Scotland — schod 
in that of Cornwall — albite in the plutonic rocks 
of the Andes — common felspar in those of Eu- 
rope. In one part of Scotland, the mica^schist is 
full of garnets ; in another it is wholly devoid of 
ihem : while in South America, according to Mr. 
Darwin, it is the gneiss, and not the mica-schist^ 
^hich .is most commonly garnetiferous. And not 
pnly do the proportional quantities of felspar, 
quartz, mica, hornblende, and other minerals, 
vary in hypogene rocks bearing the same name; 
but what is still more important, the ingredients, 
33 we have seen, of the same simple mineral 



Cb.XXY.3 WHY LSSS CALCAREOUS 52S 

are not always constant, (p. I47.9 and table^ 
p. 166.) 

The Metamorphic straJta^ why less calcareous thani 
fkefossiliferous. — It has been remarked, that the 
quantity of calcareous matter in metamorphie 
Strata, or, indeed, in the hypogene formations ge« 
nerally, is far less than in fossiliferous deposits^ 
Thus the crystalline schists of the Grampians in 
Scotland, consisting of gneiss, mica-schist, hom-» 
blende-schist, and other rocks, many tliousands of 
yards in thickness, contain an exceedingly small 
proportion of interstratified calcareous beds, al-' 
though these have been the objects of careful 
search for economical purposes. Yet limestone 
is. not wanting in the Grampians, and it is 
associated sometimes with gneiss, sometimes with 
mica-schist, and in other places with other mem-^ 
bers of the metamorphic series. But where lime- 
stone occurs abundantly, as at Carrara, and in 
parts of the Alps, in connection with hypogene 
rocks, it usually forms one of the superior mem-^ 
bers of the crystalline group. 

The scarcity, then, of carbonate of lime in 
the plutonic and metamorphic rocks generally, 
seems to be the result of some general cause. 
So long as the hypogene rocks were believed 
to have originated antecedently to the creation 
of organic beings, it was easy to impute th^ ab- 
sence of lime to the non-existence of those mol* 



526 SCARCITY OF LIME (Tart a 

lusca and zoophytes by^ which shells and corak 
are secreted ; but when we ascribe . the crys- 
talline formations to plutonic action, it is natural 
to inquire whether this action itself may not tend 
to expel carbonic acid and lime fix>m the materials 
which it reduces to fusion or semi-fosion. Although 
we cannot descend into the subterranean regions 
where volcanic heat is developed, we can observe 
in regions of spent volcanos, such as Auvergne 
and Tuscany, hundreds of springs both cold and 
thermal, flowing out from granite and other rocks, 
and having their waters plentifully charged with 
carbonate of lime. The quantity of calcareous 
matter which these springs transfer, in the course 
of ages, from the lower parts of the earth's crust 
to the superior or newly formed parts of the sam^ 
must be considerable.* 

If the quantity of siliceous and aluminous in- 
gredients brought up by such springs were great, 
instead of being utterly insignificant, it might be 
contended that the mineral matter thus expelled 
implies simply the decomposition of ordinary sub- 
terranean rocks ; but the prodigious excess of car- 
bonate of lime over every other element must, in 
the course of time, cause the crust of the earth 
below to be almost entirely deprived of its calca- 
reous constituents, while we know that the same 

I • See Principles, Index^ " Calcareous Springs,** 



Cb* XXV*] IN MBT AMORPHIC ROCK& 527 

action imparts to newer deposits^ ever fotming in 
seas and lakes, an excess of carbonate of lime. 
Calcareous matter is poured into these lakes and 
the ocean by a thousand springs and rivers; so that 
part of almost every new calcareous roek chemi- 
cally precipitated, and of many reefs of shelly and 
Coralline stone, must be derived from mineral mat*' 
ter subtracted by plutonic agency, and driven up 
by gas and steam from fused and heated rocks] in^ 
the bowels of the earth. 

Not only carbonate of lime, but also free car- 
bonic acid gas is given off plentifully from the 
soil and crevices of rocks in regions of active and 
spent volcanos, as near Naples, and in Auvergne. 
By this process, fossil shells or corals may often 
lose their carbonic acid, and the residual lime may 
enter into the composition of augite, hornblende, 
garnet, and other hypogene minerals. That the 
removal of the calcareous matter of fossil shells is 
of frequent occurrence, is proved by the fact of 
such organic remains being often replaced by silex 
or other minerals, and sometimes by the space 
once occupied by the fossil being left empty, or 
only marked by a faint impression. We ought not 
indeed to marvel at the general absence of organic 
remains from the crystalline strata, when we bear 
in mind how often fossils are obliterated, wholly or 
in part, even in tertiary formations — how often vast 
masses of sandstone and shale, of different ages, 



528' METAMOBPHIC HOCKS. ' [VwAW. 

and thousands of feet thick, are devoid of fossils —^ 
how certain strata may first have been deprived of 
a portion of their fossils when they became semi* 
crystalline, or assmned the transition state of Wer< 
ner — and how the remaining organic remaiiis 
may have been ef&ced :^hen they were rendered 
metamorphic. Some rdcl^ of the last-mentioned 
class, moreover, must have been exposed again 
and again to renewed plutonic action. 



INDEX. 



A. 

Aberdbbnsmrb, granite of, 203. 

Acephalous moUusca, 60. 

Acrodus nobility 389. 

Aetfnocerat Simmsii^ 463. 

ActinoAte, 166. 224. 

Agassis, on fossil fish, 309. 388, 389. 409, 

416. 426. 454. 
Age of aqueous steita, how determined, 

2ri. 

, of Tolcanic rocks, 467. 

— -^ of the plutonic rocks, 487. 
-— ^, of the metamorphlc rocks, 609. 
Airdnamurchan, trap veins in, 171. 
Alblte, 166. 
Alluvium described, 131. 

passes into regular strata, 133. 
>, marine, 135. 
Alps, reversed position of strata in, 1 13. 

518. 
— *, curved strata of, 114. 
, metamorphic rocks of the, 497. 

516. 
Altered rocks, 17. 176.204. 235. 241. 495. 

609. 
Alternations of coarse and fine strata, 

how formed, 8. 33. 
— — , of marine and freshwater forma- 
tions, 68. 
Alumine in rocks, how to detect, 28. 
Amblyrhynehtu crittaim^ 395. 
America, Recent and Tertiary strata 

of, 295. 
»— Silurian strata hi, 462. 
Amici, Professor, on recent Chars, 67. 
Ammonitet, figures of, 327. 879. 410. 425. 
Ampelite, 226. 
Amphibolite, 161. 225. 
AmpnUaria gUmca^ 64. 
Amygdaloid described, 155. 



Ananchytes ovatuit 318. 

Ancyltts eleganSt 62. 

Andes, geological structure of, 494. 

, tertiary plutonic rocks of, 495. 

Anglesea, rocks altered by a dike In, 

176. 
AnodontOt figures of, 61, 
Anopiotheriumt 311. 
Ansted, Mr., on Cambrian fossils, 465. 
Anticlinal line explained, 101. 110. 
Antrim, rocks altered by dikes in, 175. 

, on age of trap rocks of, 480. 

Apennines, age of metamorphic rocks 

of, 513. 
Apes, fossil, 311. 
Apiocrtniies roiundta, 373. 
Aqueous rocks described, 6. 271. 
Arbroath, section fk-om, to the Gram* 

plans, 99. 
Arenaceous rocks described, 26. 
Argillaceous rocks described, 27. 223. ; 
Arran, dikes in, 171. 

, geology of, 506. 

, section of, 507. 

Arthur's seat, strata altered in, 179, 
^«apA«»,figures of, 4*^. 461 . 
Ashby, faults in coal-field of, 128. 
Ashes, volcanic, hollows filled up fay, 
• 40. 

, wide dispersion of, 472. 

AitarU, 305. 
Atlantis, 363. 
Auch, ape fossfl near, 312. 
Auglte and homUende, analogy of, 148. 
— — , analysis of, 166. 
Augite rock, 161. 
Augitic porphyry, 161. 
Auricula^ 62. 

Autreppe, unconformable strata, 115. 
Auvergne, volcanos of, 11. 145. 477, 
— , f^esh water strata of, 88. 
A 



530 



INDEX. 



AuTergne, rocks deoovpoied by car- 
bonic add in, M8. 
— ^ tertiary red sandstone of, 419. 
— , calcareous springs of, 596. 
AHcula, figures of, 885. 4ia 



JBaeiOaria in tripoU, 5S. 
BaemlUe$t figures of, 317. * 
Bakewell, Mr., on stmetore of rocks, 

234. 
Bala limestone, 465. 
Baltic, rocks drifted by ice in, 138. 
Basalt described, 158. 161. 
__, columnar, 18S. 
-.^, sandstone rendered columnar by, 

235. 
.1— and trachyte, relative position of, 

474. 
Basin, or trougb, described, 100. 
Basset, term explained. 111. 
'Bayfield, Captain, on transportation of 

rocks by ice, 138. 
.— .i— , on worn limestone pillars, 335. 
Beaumont M. E. de, on lias of the Vos- 

ges, 387. 
^ on metamorphic rocks in the Alps, 

* 497.518. 

Beck, Dr., on recent and tertiary fossil 

* 8heUs,287. 
. on classification of tertiary strata, 

289. 
, , on proportion of species to genera 

in different latitudes, 290. 
^ on stones carried by sea- weed, 323. 

, on Graptolites, 461. 

Belemnites, figures of. 317. 379. 
Bellerophon eottatnt, 488. 
Beremcea diluvfanat 374. 
Berger, Dr., on dikes in chalk of Antrim, 

176.481. 
BeVgmann on trap rocks, 142. 
Bernese Alps, sections in, 519. 
Berthier, on augite, 149. 
TBertrich-Baden, globular structure in 

basaltic columns at, 185. 
Berwickshire, curved strata on coast of, 

101. 
Biggleswade, section near, 88. 
3illn, tripoli of, composed of infiisoria, 

52. 
Binstead, fossils of, 311. 
Birds, fossil, in Wealden, 350. 
Bischoff, Professor, cited, 247. 
Blainville, on number of genera of mol- 

lusca, 60. 
Boate, Dr., cited, 201. 253. 



Boblaye, M., on geology of t&e Itorea, 

842,481. 
Bog iron-ore, infiisoria fi)ssil lUi 54. 
Bonpland, cited, 433. 
Bothnia, Gulf of, proofii of rise of land 

in, 95. 
Bou£, Mr., his classification of rocks, 

268. 

, on metamorphic rocks, 514.^18.- 

Bowerbank, Mr., 319. 

Bradford clay, fossils of, 373. 

Brash described, 130. 

Bray, valley of, 315. 362. 

Breccia, volcanic, 159. 

Bridgnorth, tertiary strata of, 298. 

Brongniart, M. Alex., on vertical trees 

in coal strata, 445. 
Brongniart, M. Ad., on fossil coal plants, 

426, 427. 429, 430. 432. 
, on climate of carboniferous period, 

438. 
Bronn, Professor, on fossils of upper 

New Red sandstone, 410, 41U 

, on Orthocerata, 462. 

Brora coal-field, 385. 

~— , granite of, 504. 

Buckland, Dr., on changes caused IhT 

dikes, 177. 
.— — , on coprolites, 321. 
— -, on origin of flint in chalk, 328. 

, on fossils of Oolite, 375. 383. 

— , on dirt-bed in Portland, 354, 355. 

357. 

, on Ichthyodorulites, 390. 

.— ', on saurians of the Lias, 393. 897. 

, on the New Red sandstone, 407, 

—— , on fossil footsteps, 412. 

, on fossil coal plants, 435. 44^. 

, his classification of secondary 

rocks, 456. 
Budenheim limestone, 59. 
BuUrmu lubHctu^ 64. 
Bunter sandstein and fossils, 409. 
Burdlehouse fossils, 424, 

C. 

Caer Caradoc, trap-tuA of, 485. " 
Cairo, strata formed by the Nile at, 7, 
Caithness, fossil fish of, 453« , 
Catamites, figures of, 433. 
Calcareous rocks described, 28. 
Calcareous springs, action of, 526. 
Caldcleugh, Mr., on eruption of Cose- 

guina, 472. 
Calytnene Bhrnienbackii^ 459. 
Cambrian rocks and fossils, 456. 465» 
.— ., volcanic rocks, 485* 



INDEX. 



SSI 



Campagna di Roma, tufl% of, 476. 

Caiital> Tolcanic rocks ol^ 477. 

Cape Wrath, granite veins of, 209. 

Cai^oc sandstone, 460. 

Carbonate of lime, 166. 

— -— , why least in oldest rocks, 525. 

Carbonic acid, in water of sediment in 

delta of Ganges, 86. 
— — , rocks decomposed by, 248. 
Cftrbonifeifous limestone and fossils, 

436. 
Carboniferous period, rocks of, 420. 
'——, climate of, 438. 
— , trap rocks of, 482. 
— T-ff Plutonic rocks of, 499« 
— >, subsidence in, 443* 
— — . See Coal. 

Carpathians, cretaceous rocks of, 333. 
'Carrara marble, altered oolite, 513. 
CaryophyUia annularis, 371. 
Castrogiovanni, bent strata near, 112. 
Casts of shells, how formed, 80* 
Catenipora etcharoidesy 460. 
CaWUui Cuvieri, 315, 316. 
fiaulopteris prinueva, 429. 
Cautley, Capt., on fossil monkey, 31 2. 
Celsius on rise of land in Sweden, 95. 
Cementing together of particles in stra- 
ta, 72, 
Cepkalaspit LyeUii, 454, 
CeratUes, 410. 
Cerithiumcinctum^ 63, 
Charopatamntt 311. 
Chain-corals, 460, 461. 
Chalk, white, composition, &c.,' 28. 314. 
n , fossils of, 55. 315, 316. 319. 321. 

339. 
— — , origin of Uie, 319.- 

, pebbles in, 322. 

»-— , its extent, 929. 
^-— , external configuration of, 334. 
— *-, needles and escarpments of, 334. 
«— , greatest height of, in England, 

337. 
Chalk-flints, infUsioria in, 56. 
^— , origin of, 327. 

Chalk formation, its marine origin, 313. 
— , stibdivlsions of, 314. 
-_, fossUs of, 815. 319. 381. 339. 341. 

, geographical extent, 329. 

•— , difference of, in north and south 
. of BuR^e, 837. 

— — • map of, In S. of France, 338, 
•— , altered by granite, 245. 

., covered by granite, near Meissen, 

505. 
«— , alternating with volcanic tuff. 479, 

480, 500 Cretaceous, 

AA 



Champoleon, junction of granite and/ 

secondary rocks near, 497. 
CAane, fossil, in fireshwater strata {tee 

Jigutes)., 66. 
Charlesworth, Mr., on the crag, 300/ 
Charpentier, M., on trap rocks of 

Pyrenees, 480. 
Cheese-grotto, at Bertrich-Baden, 185. 
Chemical deposits, 70. 
Cheshire, ripple-marked sandstone 

from (see fig. 6) .,41. 
Chevalier, M., on bent coal strata near 

Mqus, 105. 
Chiastolite, 166. 
Chiastolite-slate, 225. 
Chitncera moiutrosa, 890. 
Chimney, the, hasaltic dike in St* 

Helena, 183. 
Chirotherium, 412. 
Chlorite, composition of, 166. 
Chlorite-schist described, 224. 
Christiania, dikes near, 173, 174. 
— — , granitic rocks of, 212, 213. 215. 
<— >, passage of trap into granitic rocks, 

near, 203. 
— — , porphyry conformable to strata, 

near, 215. 
— — , rocks altered by granite, neari 

242. . 

, tertiary stra,ta, near, 295. 

Cidaris ctmmaiat 377. 

Ciply, cretaceous rocks at, 326. 

Classification of rocks, principles oi| 

which it is founded, 4. 24. 
, of the fossiliferous rocks, 268. 2794. 

456. 
Clay described, 27, 
Clay-slate described, 223. 
.: — , lamination of,-iQ the IVrenees^ 

229. 
— -, position of| in the metamorphia 

series, 522. 
Claystone, and Claystone porphyry,. 

161. 
Cleavage pf rodu, 230. 
Climate of carboniferous period, 438. 
Clinkstone, 162. 230. 
Club-mosses, 482. 
Coal, vegetable origin of, 57. 422. 

, fossils of the, 422. 

strata, origin of, 422. 441 . 

— , on vertical trees in, 57. 444. 

, isolated patches of, 441. 

— , rate of deposition of, 445, 450. 
, zigzag flexures of, near MoiiS| 

105, 
~~. <Sf0 Carboniferous, 
Coal-pipes, 447* 

2 



ssc 



Goilteook dale coaUMd; 4M» 
Cockfleld FaU, coal turned into wot by 

aik«at,118. 
Columnar etnicture In ro^a, Ul» 197. 



76. 



•— , la ke, 296. 
C o l u mmari a cblonga, 871. 
Compart Iriepar, 168. 
Concretionarj itniokttre in 

77. 
Conea and cratere» 1k>w foruMd, 14S. 
Cong ji omertea d ai tr fce d , >7. 
— , Tertica], in Scotland ftc, 96. 

, of New Red sanditooe, 414. 

Conifers, fouil. 8S. 43S. 438. 
ContoUdation ef itrata, 70. 
Cenybeara, Ber. W.D.,on&ulCt,lSl. 

; li9. 

, on dianget cauaed by dikea, 177. 

— » on the Chalk fbmntion, 314. 

— , on the Pleileaanraa, S&l. 

— , on the OeUte and Lias, 887. 400. 

—- .^ on the New Bed candstone, 407. 

.— ., OB the Goal itraita, 488. 

Coprolitea of the Chalk, 321. 

Ceral iakmdt, drngea of level fai, 96, 

97. 
Coral raflr, fcaaila of the, 871. 877. 
Coral reeft, great extent of, 329. 
Corals. foMlI, 808. 371, 372. 
Corbula aiata, 347. 
Comean* IfiS* 
Cornwall, itracture of granite of» 196. 

199. 
— », granite Teins ki, SIO. 244. 
Coseguina, volcanic eruption of, ^2. 
Cotta, Dr., on granite of Wdnbohla, 

605. 
Crag formation, and ki foMlIs, 800. 

306. 
•*~^ divMoB of, into red and coralline, 

300. 

, may all bdong to one period, 305. 
its relative position, 306. 
Craigleith fossil trees, 82. 44S. 
Crania, figures of, 49. 816. 
CrcutateUa tulctOa, 810. 
Craters, volcanic, how formed, 146. 
Craven fisult, 121. 
Cretaceous period, 313. 
— , volcanic rocks of, 478. 
— , Plutonic rocks of, 496. 
_-. See Chalk. 
Crop out, term explained, 110. 
Croirthome, tertiary deposits at, 298. 
Cuba, tertiary strata in, 297. 
Curved strata, 99. lOI. 
— — , experiments to illustrate, 102. 



Curved strata, origiii«<; 184. 

Cutch, changes cauaed by eart hqg efc nr 

in, 886. 
Csfothea gteutca, 4SKk 
CpaikocrmOes plmim, 419. 
Cycku ekmaia, 89. 

VfffmU OOCCtmCtt999eft <9WS. 

CM»rtf , fossil in ireahfwatar atntn, 68. 

, figures of, 348. 488. 

i^rcMi Ir^OMtfte, 60. 
Cjftkernue of the Chalk, 58. 



848; 



D. 

Dartmoor granite, 844. 

Daubeny, Dr., on the 

Dax, chaJk near, MO. 

_— , chalk and volcanic tuff altemadBg; 

near, 479. 
Darwin, Mr. C, on gradoiA rise of 

parts of S. America, 9& 

, on coral isiands, 96. 

-i— , on formation of mould, 180. 
» on shivering of reeks In ChiK \ff 

earthquakes, 180. 
, on transportation cf recka by ifie^ 

187. 189. 
.— ^ on slaty atrackore in rafbieorgdd 

Blbie,28B» 

, on structure of Andes, 494. 

- ^ on recent strata near Uma, 295. 

—, on origin of chalky mod in Padio^ 

321. 
.-^ on drifting of atonea ta nota of 

treds,322. 
.-^ on stones attached to sea^^eed, 

824. 
_, on living saurian of the Gataya- 

gos, 394. 

, on subsidence in Pacific. 408. 

De la Beche, Mr., on c ajra r rwis no* 

dules in Lias, 76. 

, on rocks altered by granite, 848. 

, on dirt-bed ha. Portland, 384, 866< 

357. 

, on saurians of the Lias, 393. 898. 

-^^ on trap rocks of New Bed sand 

stone, 481. 
..., on metamorphic rodis, U4. 
Delta of Indus, recent changes In, 3B6. 

, the Niger, its sixe, 861. 

Deluge, fossils attributed by iobm to, 9. 
Denmark, cretaceous coral reef in, 384. 
Denudation defined, 184. 

^ its great amount, 1%. 

, valleys of, 126. 

— ., on a great scale in Boss-shire, 127. 
, proofk of, from levdled sorfiMe o£ 

districts where great fisulti occur, 187. 



INDEX. 



533 



Denudadoo, connexion of alluvial form- 
r ations, and, 129. 

>-— , pioofs of from trap-dikes. 189. ^ 
Deshayei, M., his identification* of re. 

cent and fossil sheUs, 284. 288. 306. 
2>eoxydation of mineral waters by or* 

ganic matter, 85. 
Devonshire, trap vocka of, 481. 
Diagonal stratification explained, 38. 
Diallage, 166, 
Diallage rock, 162. 
Diceraa ff/rieHnot VTl. 
Diceras limestone, 378. 
Diddpkiftt fossil, 388. 
Dikes, volcanic, described, 12. 168. 

, mora crystalline in the centre, 172. 

— , fragments of subjacent rocks in, 

174. 
— — , changes caused by, 13. 18. 170. 175. 
— — , granitic, 207. 

Diluvium, ancient aUuviums called, 134. 
Dimyary moUusea, 61. 
Diorite anddioritic pondiyry, 162. 
Dip, term explained, 105. 
, how to measure, 108. 
— , reversed, how caused, 113. 
Dirt-bed in isle of Portland, 353, 
Dolerlte described, 154, 162. 
Dolomite described, 31. 
Dolomitie conglomerate, fossils of, 415. 
Domfte, 163. 

Drift-wood of American rivers, 449. 
Dudley, altered coal shales of, 244. 
JDufkffooy, M« on rocks altered by gra- 
i liite,245, 

E. 

Earth's crust, term explained, 3. 

— — , oomposed of distinct substances, 3. 

— , its successive formation, 2. 

, arrangement of its materials, 3. 

— «» not inereasing in thidmess, 967» 
Bekifti tnm the Chalk, parasitic fossils 

on, 48, 49. 
Edinburgh coal-field, fosiOs of; 424, 426. 
Ehrenberg, Professor, on inftuoria, 51. 

54. 56. 
Eifel, volcanic rocks of the, 477. 
Elbeuf, needles and grooved pillars of 

chalk at, 335. 
Elevation of land, gradual, prooft of, 93. 
Enerhtite$ fossil fai OoUte, 873, 374. 
EndotipkomUei eariiuUms, 465. 
England, tertiary strata of; 296. 811, 
Bnstone, fossil bone fh>m, 883. 
Eocene, term whence derived, 285, 
-^'•ttata, iiLBnclvid, 908,.* 



Eocene yolcanic rocks, 477. 

Epidote, 166. 

EquUetacea, 409. 427. 432. 439. 

Erratic blocks, distribution of, 135. 

— •, transported by ice, 136. 

Escarpments of ooUtes, &c., 4C4. 

Eschara disiickot 318. 

Estuary deposiU, 6. 

Etna, lavas, tuflk, and dikes of, 471. 476, 

Eunomt'a radiata, 372. 

EuphorbiacetBt 434. 

Euphotide, 163. 

Eurite and euritic porpyhiy described. 

202.225. 
Exogyra bulUit 847. 

F. 

Falconer, Dr., on fossil monkey, 312. 

False stratification explained, 38. 

Paacicttlaria aurantium, 304. 

Faults described, 117. 

cause apparent alternations of 

strata, 119. 

— , great amount of some, 120. 129. 

.origin of, 119. 121. 

— , grooved autSacea of; 121 . ? 

, denudation proved by, 127. 129. 

Faxoe limestone and its fossils, 324. 
Felspar, varieties of, 147. 166. 

• , its decomposition aflbrds silex in 

solution, 88. 
Felspar-porphyiy, 163. 

Findheim, land shells in limestone of^ 
08. * 

Fish killed by submarine eruptions. 

floods, &€., 399. 
Fissures, poUshed surfaces of, 116. 121. 
Fitton, Dr., on the Green-sand, 814. 

331, 332. 

, <m the Maestridit beds, 327. 

— . on the Wealden strata, 345, 846, 
358. 361. 

— •, on the Portland dirt-bed, 364« 

355,356,357. 
Fleming, Dr., on fossil fish of Old Red 

sandstone, 454. 
^— , on trap rocks, 482. 484. 
Flint, sponge fossU in, 319. 

, In chalk, its origin, 327. 

FlSta rocks of Werner, 868. 
FooUteps, fossU, 411, 412. 
Foraminifera of the Chalk, 55. 
Forikrshire, geology of, 99. 463, 

, decomposition of rodu in, 418. 

Formation, term explained, 6. 
Formations, fosllliferous, arrangement 

of, 268. 279. * 

Forth ooal-fleld, trap rocki of, 488, ' 
AS 



534 



INDEX, 



Fortis, on columnar basalt, 185. 

Fouil, term defined, 8. 

FoMlls in ttradfled nx^, 8. 

, faeiffat atwMch they are foimd, 8 ; 

— ., their arrangement in strata, 44. 

— — , parasi t ic, prove gradori deposi- 
tion, 46. 

fresliwater and marine, 88. 
tMr atoscooe in some rocks, how 
explained, 73. SW. 

mineralisation ef, 79. 
casts and impressiaiis of, how 
filrmed,80. 

FossiUferoos strata, conTwsion of into 
metamorpliic rodu, 513. 

-»^ why most calcareoos, 525. 

Foumet, H., on disintegnUion of rocks, 
248. 

Fox, Jtr. R. W., his experiments on 
lamination, 389. 

Fox, Rer. W. D., on fbssil iwannwHg, 
811. 

Freshwater formations, how distin- 
guished from marine, 58. 
, land shells numerous in, 58. 

, fossils numerous, but species few 

in, 60. 

— , figures of shells most common in, 
60, 61, 6B, 63. 

Cypris fossil in, 64. 
Chars fossil in, 66. 

, rertebrated animals in, 67, 68. 

••— •, alternating with marine, causes 
of, 68. 

Freshwater strata of the Coal, 422. 441. 

Frontispiece described, 19. 

Fmnti cowhrarhu^ 303. 

Gabbro, 163. 

GaiUoHeOa, fossil in tripoli, 52. 54. 

Galapagos islands, liring marine reptile 

of, 393. 
Ganges, river, deposits fa estuary of, 6. 
Garnet. 166. 

— , in altered rodts, 176. 624. 
Gases, subterranean, rocks altered by. 

248. 

Gault, 330. 

Gavamie, curved strata near, 116. 

Geology defined, 1. 

GesteUihorn, section at base of the, 519. 

Giant's Causeway, volcanic rocks of, 13. 

Glen Tilt, junction of granite, schist, 

and limestone in, 204. 206. 
Globular structure, 182, 
GnelM described, 220. 
G^mtoe. slaty structure in reftue of, 



Gtmiatites evoimimg, 438. 

Goppert, PioC, his experiments e» fu- 

silixation of irfaots, 64. 
Gosforth, tree fa coal strata at, 82, 44^. 
Graham island, 191. 
Grampians, vertical eoi^aiBMates in 

the, 98. 
— , section from to^the aea, 99. 
— , dikes of granite fa, W« 
— — , deoompoMd rocks ct, 418^ 

^, rarity of limestones fa the, Sai. 

Granite, of Igneoos origin. If, 2H. 

, of difSBrent ages, 99. 906. 487. 

, general aspect, straetoiR, ad 

compositloB of, 196. 
-— , varieties of, 199. 

, passage from tr^ to, 963. 

• — , analogyfa composition of tradvte 

and, 204. 
— , veins, 204. 

, finer grained fa vefas, 209. 

, isolated masses of, 213. 

, wiiether it ever everiies fossSiiis* 

rous rocks, 315, 605. 
, rocks altered by, 15. 943. 244. 4S4. 

501. 
-— , oq the most ancient, 503. 

, protrusion of solid, 504, 505. 

, of Arran, age of, 506u 

. See also Plutonic rocks, and Hy* 

pogene rocks. 
GrajAic granite described, 199. 
GrapMites^ 462. 
Grateloup, Dr., on dialkof S.of I^raneet 

340. 
Grauwack§, term, 455. 
— — , difibrent ages of, 455. 
Graves, M., on valley of Brqr, 368. 
I Gray, Mr., cited, 62. 
Greenland, subsidence oi part of, 96. 
Green-sand formation, 330. 

, fossils of, 331. 

^— , its origfa, 332. 
Greenstone described, 154. 163. 
Greystone, 163. 
Grit defined, 37. 

Qtyfduea^ figures 0^147.376. 388« 
Gryphite limestone, 388. 
Guadaloupe, hdman flkdeteoa of, 296w 
Gnidoni, M., on altered oolite^ 514, 
Gosigny, section at, 115. 
Gypsum, compositiott of, 33. 
GyrogonHet, 66. 

H. 
Haiy, Sir J., on curved strata, 101, 103. 
Hall, Capt., B. on dikes fa Madeiia, 

169; 
— ^, on granite veins, 909^' 
A 



IHDEX* 



535 



HamHet spinier, SSL' 

Harwich, aectlea in cliA at, 309. 

Hastings Sand, 345. 369. 

Heat, consolidating effects of, 79. 

Hebrides, trap rocks of, 481. 

BeidettMHTg, granites of different ages 

vat, 906. 
Helix plebeimn, fit. 
Henry, expeifcnentt of, S47, 
Henslow, Prof., on changes caused by 

a dike in Anglesea, 170* 

, oa tbe Portland dirt-bed, 355. 

Herschel, Sir J., on slaty degvage, 239. 
Hertfordshire puddingstone, 73. 
Hewett, Capt., on new channel in Yar- 

mwth sands, 307. 
Hibbert, Dr., on fossils of the Coal, 425. 
High Teesdale, gvnets in altered rock 

at, 176. 
•f—, intrusion [of trap between strata 

at, 181. 
Hildburghausen, fossil footsteps at, 411. 
Hippmrita, figures of, 338, 340. 
Hoflknann, on agency of subterranean 

gases, 249. 
—— , on metamorphic rocks, 514i 
Hoogly, R., analysis of water contained 

in mud of, 86. 
Hornblende, 148. 167- 
Homblende.jrock, 163. 225. 
Homblende-scbist described, 822. 
Homstone, homstone-porphyry, 163. 
Horner, Mr., on fossil fish in Coal 

strata, 425, 426. 
—— , on the Malvern hills, 500. 
Hubbard, Prof., on granite Teins, 490. 
Hiigi, M., on alternation of gneiss and 

fossiliferous rocks in Alps, 618. 
Humboldt cited, 433. 
Hungary, tradiyte of, 204. 
Huttoo, opinions of, 261. 
Hutton, Mr., on fossil coal plants, 427. 
t 434.447. 

Hybodta reticttlahu, 389. 
Hypersthene, analysis of, 167. 
Hypersthene rock, 163. 
Hypogene, name proposed instead of 

primary for the crystalline rocks, 23. 
_, rocks described, 196. 224. 
— ., must be old before they reach the 

' surfkce, 620. 

1 age of, how determined, 487. 511. 

— , uniformity of mineral character 

in, 523. 
»-, why less calcareous than the fossi- 
liferous, 525. 
.1 — See also Granite, Plutonic rocki, 
and Metamorphio rocki. 



I. 

Ice, transportation of erratic blocks by, 

136. 138. 
•'— , columnar structure oi; 235, 
Ichthyodorulites, 389. 453. % 
IchthyosaurtUt 391. 
Iguanodon, 349. 363.; 
Inclined and vertical stratification, 98. 
Indus, recent changes in delta of, 36& 
Inilisoria in tripoli, &€., 61. 

, figures of, 62, 631 

Inkpen Beacon, 337. 

Insects, fossil, 382, 383. 

Inverted position of strata, how caused, 

113.' 
Ipswich, section near, 302* 
Ireland, tertiary strata in, 298. 
Ischia, tertiary strata in, 476. 
Iselten Alp, curved strata of the, 114. 
Isle of Bourbon, eruptions in, 491. 
Isle of Wight, tertiary strata of , 58. 31 1 . 
^— , chalk needles of, 336. 
Isomorphism, theory of, 151. 

J. 

Jackson, Col., on columnar structure 

in ice, 235. 
Jointed structure of rocks, 231, 
Jorullo, volcanic eruption of, 490, 
JungArau, section on the, 519. 
Jura, section of structure of the, 109. 
, OoUte of the, 369. 376. 401. 

K. 

Kander, R., land iihells in delta of, 69. 

Kaolin, mineral composition of, 27. 

Kaup, Prof., on fossil footsteps, 412. 

Keilhau, Prof., on Greenstone dike, 174. 

—- , on granitic rocks of Norway, 212, 
213.215.244.501. 

Kelloway rock, cementing of the part- 
tides of, by lime derived from shells, 
72. 

Keuper sandstone, fouils of, 409. 

Kildonan castle, dike near, 171 . 

Killas altered by granite, 244, 

Kimmeridge clay, 381. 404. 

L. 

Labradorite, 147. 166. 

La Coupe d'Ayxac, columnar lava of, 

183. 
Lakes, arrangement of deposits in, 6. 
Lamarck, his division of bivalve mol- 

lusca. 61. 
]Land, proofs of the elevation and suIn 

sldenceof,91,96. 
Lander, Mr., on delto of Niger, 362, 
X«nd*i BnA» gnmtto o^ 197. 199, 



586 



IKDSX^ 




Land ihelb, Bomcront In frcthwater 

tormrtloni, flft> 

, drifted bf ilren, 80. 
flgUTM of gener* most oonunon 

lnitraU,64. 
Lartet, M., oo fotsfl ape, 311. 
Lateral morementi, folding of itrata 

JV.104. 
Lava deicrfbed, 145. 157. 
Lehman's diviakm <rf rocks, 857. 
Leibnits, theory of, 965, 2G6. 
Lqmiodembra, eguret of, 431. 
LqMoimJigaieg ot, 349. 388. 
Leodte, 167. 

Liat, mineral character of, 386, 387. 
— — , fofsils oi;— shells, 386. 396 ; — fish, 

888 ; —reptiles, 390 ; — plants, 399. 
and Oolite, origin of, 399. 
▼aUeya and escarpments ibrmed 

by, 408. 

calcareoas oodoles in, 77. 
Tolcanic rocks of the, 481. 
plttton&e rocks of the, 497. 
Lima. Beoent strata near, 895. 
Lime in rocks, how to detect, 99* 
"t^t whence deriTod, 87. 
—— , why less in crystalline rocks, 525. 
Limestones, composition of, 88. 45.. 
■ ■ , deposited by springs, 71. 
, in coral redk formed bgr soophyta, 

71. 
Umnea hmgiscaia, 62. 
Lindley, Mr., on fossil coal plants, 427. 

489, 430. 434. 439. 447. 
^-» on destnictibility of pUmts in wa- 

ter,440. 
LIpari islands, rocks altered by gases 

in, 249. 
Llandeilo formation, 460. 
Loam described, 30. 
Loeu of the Rhine, 297. 
- — , tuflk hiterstratified with, 477. 
Loire, R., stratification of recent mud 

of, 34. 
London day and its fossils, 49. 306. 
Lonsdale, Mr^ on microscopic chalk 

fossils, 55. 
-i^ on Stonesfield date, 382. 
I<ons.le-Saalnier, Lias and Oolite of, 

887. 
Louisiana, submerged trees in, 450. 
Lower New Red sandstone, 418* 
Ludlow formation, 458. 
Lulworth coTe, section in, 356. 
Lumley Den, trap rocks in, 484. 
Ltttschine, Talley of, cunred strata in. 

114. 

Xif«?pa*«ofte, 427. 431, 438. 439, 440. , 



LynuFlord, faiTaded by the sea, 69. 
—, itcnea carried by sea-weed in, 38&> 



tfacCuIloch, Dr., termed volcanicfQcks 

overlying, 17. 
_-, <m coosoUdation of strata, 74* 
^— , OQ denodation, 186. 

, on compact fe^iar* 148« 

— ^ on trap rodLs and dikes, 170^ 171. 

193. 
— — , on columnar basalt, 182. 
, on passage of granite into tn^ 

203. 

» on granite veuis, 205. 208, 809. ^ 

, on altered rocks, 179. 858. 498. 

— — , on isle of Arran, 510. 
Madieira, dikes in, 169. 
Maestricht beds and their HDSsfls, 326. 
Magnesian limestone and Ibasils, 414** 

417. 
, composition of, 31. 
— — , ooncretkmary structure fan, 77. 
Bfalvem hills, rocks altered by granite 

in, 500. 
Mammalia, extinct, found with living 

shells, 297. 899. 
Mammat, Mr., on faults anddenndakioB 

in Alhby ooal-fidd, 128. 
Mammoth, fossU, 297. 899. 
ManteU, Mr., on fossils of the Chalk, 

323. 327. 
— — , on the Iguanodon, MS» 
^— , on Portland dirt-bed, 854. 
— , on plants of the Wealden, 360. 
Map of chalk in south of France, 388. 
Marble described, 29. 284. 
Margarate, term expUdned, 840. 
Marine formations, how distinguished 

firom fresh water, 5S. 
Markerud, strike of beds not altered 

by intrusion of granite at^ 818. 
Marl and marl-slate described, 30, 31, 
Mechanical dqiosits, 70. 
MegaUcktk^ HMerti^ 486. 
Meissen, granite covering chalk, near, 

505. 
MelanopUt bueeinoidea, 62. 
Melaphyre, 168. 

Menai Straits, tertiary strata near, 898. 
Mesotype, 167. 

Messeaia, puddbagstone of, 8tt. 
Metalliferous veins, 818. 
Metamorphic, term whenee derived, 19. 

rocks, general character of, 819. 

— — , prindpal members of tlUs cl«a 

described, 220. 

—» their origiB, 17. 896.811. 96a« " 



IUfBEt!, 



537 



of. 



Metamorphic roclfai, stxat]ficatioii. 

distinct from.cleairsge, SSO. 
* — , kind of strata from whicli some 

may have been derived, 292. 
— , on the different ages of, and how 

detwmteed, 509. 

of the Apennines, Alps, &c., 513. 
> most be (dd before they reach the 

aorftoe, 52a. 
— , order of succession in, &2I. 
— , why les« calcareous tlian the fos- 

lUlferoas, 586. 
Mie(yrixj«en, section near, 519. 
Mica, deosmpoftition of, aflbrds sUex in 

8olHtion^89. 

, composition of, 167. 

Micaceous sandstone described, 26. 

Mica-sohist described, 222, 225. 

Mieroconckust 423. 

Miller, Mr., dted, 418. 

Millstone grit, 421. 

Mineral character as a test of age of 

rocfcs, 293.472.488.511. 
Minerals in volcanic rocks, analysis of, 

266. 
Mineralization of organic remains, 79. 
Mingan islands, worn limestone pfilars 

in, 335. 
Miocene, term whence derived, 285. 
— - deposits not found in England, 

300k 
— volcanic rocks, 477. 
Ififlsissii^, R., deposits in estuary of, 6. 
—— , lagoons alternately fresh and salt 

at mouth of, 68. 
*— , drift wood of, 449. 
— p., delta of, 451. 
MUra fcabroy 810. 
Mitscherlich, Professor, on anglte, 

149. 
— , his theory of Isomorphism, 151. 
Moel Tryfane, tertiary strata on, 298. 
Monkey, fossil, 312. 
MoDomyary mollusca, 61 . 
Mobs, xigsag flexures of coal near, 105. 
— , unconformable strata near, 115. 
Morea, cretaceous rocks of the, 342. 
.f— , volcanic rocks of, 478. 481. 
3/otasaflfntf, 327. 
Moiild, formation of, 129. 
Mountain nmestone and fossils, 421. 

436. 
Mount Battock, granite dikes in, 207. 
Munster, Count, on Solenhofen fossils, 

381, 
..^— , on fosrils of the Keuper, ftc, 409. 
Murchison, Mr., on joints and slaty 
dMvaf e, 231. 237* 



Murchison, Mr., on tertiary strata, 298^. 

, on Brora coal.field»w5. 

1 on New Red sandstone, 408. 

414. 

, on fossils of the Coal, 423. 

, on Old Red sandstone, 452. - 

, on the SUurian strata, 456. 458. 

460. 

— — , on Silurian and Cambrian trap- 
rocks, 484, 485. 

, on granite of Dartmoor and Mal- 
vern hills, 499, 500. 

, on granite of Brora, 505. 

— , on geology of Arran, 510. 

Mtarex alveolatus, 303. 

Muscbelkalk, fossils of, 408. 

^' 

Nsesodden, greenstone dike of, 173. ' 
Naples, tertiary strata of, 298. 
Nassa grtuutlaUit 303. 
Nautiius, figures of, 310. 388. 
Necker, Mr. L. A., terms granites un- 
derlying igneous rocks, 17. 251. 

, on metalliferous v^s, 212. 

— , on the Valorsine, 213. 215. 
— ^ on metamorphic rocks of th 

Alps, 518. 
Needles of chalk, 334. 836. 
Nelson, Lieut., on chalk formed by de 

composition of corallines, 320. 
Neptunian theory of the origin of rocks* 

260. 
Neriiuea^ figures of, 877. 
Nerinsui Umestone, 378. 
Neriia gr»nulo9s^ 63. 
Neritina globulus^ 63. 
Newcastle coal-field, great faults in; 

120. 129. 
New Red sandstone group of rocks,' 

406. 

, position and subdivisions of, 407. 

, origin of the, 418. 

New Zealand, 366. 442. 

Niesen, slates of the, 237. 

Niger, R., delta of, 361. 

Nile, R., stratified deposits formed 

by. 7. 

, lagoons at mouth of, 68. 

Ninety-fathom dike, 120. 

North cliff, tertiary strata at, 299. 

Norway, tertiary strata of, 295. 

, granitic rocks of, 212, 213. 215. 

242. 
— — , Silurian strata in, 461. 
Nummulite limestone, 341. 
Nutnmulites, figures of, 341. 
Nyoe, new island destroyed by tea, 19K 



538 



INDEX. 





ObddUn, 164. 

OcynhaoMn, M., on granite Tebu, 210. 
^— ^ on iile of Arran, 510. 
Old Red nndstoiie, ito rabdiTitionf 
and foMtlt,45S. 
-, trap rodu of, 433. 
, teutonic rodu of the, 500. 
OUTlne, 167. 

Oolite fonnatioii, name whence de- 
rived, 89. 868. 

extent and tnbdlTitioni of, 368.] 
, fotaili, 870 to 384. 
, change! in organic life daring itf 
accumulation, 875. 

, tigni of land during, 380. 
, Tolcanic rocks of the, 481. ' 
J plutonic rocks of the, 497. 
— .» metamorphie, in Apennines and 

Alps, 614, 615. 
— and Lias, origin of the, 399. 
^-r-, Talleys and escarpments formed 

by. 403. 
OphioUtes, 164. 478. 481. 
Ophites. 164. 480. 
Oppenheim limestone, 58, 
Orbieula r^sth 379. 
Orford, crag strata near, 302. 
Organic remains, age of strata proved 

bgr. 274. 471. 
— >. See Fossils. 
Qrtkoceratt figures of, 437. 
Ortkocerata, on structure of, 462. ; 
Ottrea, 61. 316, 817. 376. 379. 
Outcrop of strata explained. 111. 
Overlying, term applied to volcanic 

rocks, 17. 215. 
Owen, Mr., on fossil bone from En- 
stone, 384. 
pxford cUy, 400. 402. 404. 

P. r 

Palceoniscuit 416. 

Palaeontology, term explained. 281. 

Palsotherium, 31 It 

falmUna, 62. 

Pampas have been raised slowly, 96* 

Parasitic fQssils, 46. 

Pareto, M., on altered Oolite, 514. 

Passy, M ., on chalk difik of Normandy, 

336. 
Patagonia, plains of. upheaved gra* 

dually, 96. 
Pearlstone, 164. 
Pebbles In chalk, 822, 
PecopteriM kmchitiea, 428. 
Ffictent figures of, 331, 425» 



Pegmatite described, 202. 

Peperino described, 159. 

Pepys, Mr., dted, 85. 

Petrifisction of fosdls, 79. 

Petrosilex, 164. 

Peyrehorade. nummulite limestone <rf. 

841. 
PAasaanellaandcastof same,80. , 
Phillips, Prof., on grooved surfaces ai 

fkulu, 121. 

on joints in rocks, 237. 
on the Coal strata, 420. 422. 425. 
— — , on the Mountain limestone, 437* 
— — , on Cambrian fossils, 465. 
Phillips, W., on composition of days, 

«7. 

— -,0DfiuiltS,121. 

PhtOadomyaJIdicmia, 379* 

Phonolite, 164. 

Phyllade, 225. . 

Phffsa^ figures of, 62. 

Piddington, Mr., his analysis of the 

water in the mud of the Hoo^y river, 

86. 
Pingel, Dr., on subsidence in Green- 
land, 96. 
Pitchstone, 164. 
PlaghUoma^ figures of, 316. 
Planorbit euomphabUy 62. 
PUnU. fossil, of the Coal, 426. 
Plas-Newydd, changes caused hy * 

dike near, 175. 
Play&ir, on rise of land in Sweden, 95. 
i— , his description of fiaults, 117, 

1 on Huttonian theory. 261« 

PUstoiaunu^ 391. 

Pliocene, term, whence derived, S85. 

, period, fieurer, strata of^ near 

Naples, 293. 

, in Norway, 295. 

— ~, in 8. America, 295. 

, in W. Indies, 296. 

— — , in valley of Rhine, 297. 

, in Great Britain and Ireland, 

298. 
— , {older) in England, 299. 
•— , volcanic rocks of, 476. 
— — ', plutonic rocks of^ why invisible, 

490. 
Plutonic action 246. 250. 
Plutonic roek«, described, 14. 195. 

, their relation to the volcanic, 15. 

.-^, name whence derived, 16. 
— , age of, how determined, 487. 
, Recent and Pliocene, why in. 

visible. 490. 
— , of dUferent periods, 490. 
— , relative age and position (^ 499* 



INDEX. 



539 



Platonic rocks. See also Hypogene 

rocks. 
PolkiUUc group; 407. 
Polished surfaces of fissures and t^ts, 

116. 121. 
Ponza islands, globiform pitchstone in, 

'187. 
Porcelain claj, 27. 

?orphyritic granite, 199- 
orphyxy described, 155. 164. 
Portland dirt-bed, 353, 355. 
Posidonomyu miHuta^ 410. 
Pozzblana, composition of, 76. 
PudUxzo, Oolite altered at, 499. 
Pressure, consolidating effects of, 78. 
Preston, tertiary strata at, 298. 
Prestwich, Mr., on the Coal strata, 424. 
Primary fosslliferous strata, 455. 
-^, horizontal in Sweden, 463. 
Primary limestone, 224. 
Primitire or Primary, term, why er- 
roneous, 21. 23. 262. 268. 
Frbducta, figures of, 416. 437. 
Profcoglne described, 201. 222. 226. 
Puddingstone described, 27. 
— — , of Hertfordshire, 73. 
—— , of Messenia, 342. 
Pumice described, 157. 164. 
Pupa muscorum^ 64. 
Purbeck beds, 345. 

Puzzuoli, elerated marine strata at, 293. 
Pyrenees, bent strata in, 112. 115. 
— , lamination of clay-slate in, 229. 
— , rocks altered by granite in, 245. 496. 

, chalk of, 337. 341. 

— ., trap rocks of, 479. 
Pyroitenic-porphyry, 164. 

Q. 

Quadersandstein, 387. 
Quadruraana, fbssil, 311. 
QuAquA-rersal dip explained. 111. 
Quartz rock or Quartzlte described. 



Quartz reins, 214. 

Quiriqulna, island of, rocks shivered by 

earthquakes in, 130. 
Quorra, R., delta of, 361. 



R.- 
Radnorshire, trap rocks of, 485. 
Ramsholt, section at, 302. 
Rancid, altered Lias at, 245. 
RathUn, dikes at, 177. 
Recent period, how separable from 
teitiaiy, 292. 



Recent period, formations of, in differ* 

ent countries, 293. 297. 

, Tolcanic rocks of, 476. 

— ^, plutonic rocks of, why invisible, 

490. 
Red sandstone and marl, origin ot, 418, 
— ^, of different ages, 419. 
^— . See also 0/tf, and jyeuF.Red sand. 

stone. 
Reptile, living marine, of the Galapagos, 

393. 
Reptiles, fossil, of the Wealden, 349, 

363. 
— — , of the Lias, 390. 

, of the Muschelkalk, 411. 

, of the Magnesian liinestone, 417, ' 

Rhine, R., land shells drifted by, 59. 

— , valley of, tertiary strata in, 297, 

Ribboned jasper, 244. 

Riley, Dr., on fossil reptiles, 417. 

Ripple mark, how formed (see Ff^.),40. 

Rock, term defined, 4. 

Rocks, all divisible into four contem* 

poraneous classes, 4. 19. 
— , aqueous, described, 5. 25. 
-^, volcanic, described, 11. 141, 
— , plutonic, described, 195. 
— ^, metamorphic, described, 219. 
1 how to detect alumine or lime in*. 

28,29. 
— , hardened by exposure to air, 74. 
— , their particles rearranged by 

chemical action, 77. 

, transported by ice, 136. 

— , how to be studied, 152. 

, altered by dikes and granite, 170. 

175. 204. 242. 245. 49b. 511. 
, different ages of the four great 

classes of, 256. 271. 467. 487. 511. 

, classification of, 4. 24. 268. 279. 

Rose, G., on hornblende and augite, 149. 
— , on composition of volcanic rocks^ 

161,162,163. 
Ross.shire, denundation in, 126. 
RosteUaridjnacroptera^ 310. 
Rother, R., buried ship in old channel 

of, 298. 
Rothli^endes, 415. 
Roththal, section in the, 519. 
Rouen, chalk needles near, 335. ; 
Rubble explained, 130. 

S. 

St. Abb*s Head,'ciirved strata near, 101. 
St. Etienne, vertical trees in Coal strata 

at, 445. 
St. Helena, basaltic dike In, 183. 
Salbands, 173. 



540 



HfD 



. BalUtmrr Craig, altaraa 
San CiMiu, b«Dt rtnU BM 
Sandstone ilaferlbed, as. 
.Sin LoroBKH Me of, Baont 



in« 1)9« 
VllSi 



Sattal» MeCiwi on the, »ld. 

Sauroid llah ofthe Coal, 496. 

Saaame on Tortteal rgmtow waffit, *W 

SotI, M., on metanunidile racks, U^ 

Sasonf , aqoeoas strata renteed eoltaii- 
nar by basatt in, il6. 

.Scania, sinking of land In, W. 

Sdiorl, analysis of, 18T. 

Schorl rock described, 901. 

Sooiesby, on rents in icebergs,. ttS. 

Seofiis described, 1A7. 164. 

ScropetMr^ on Auvergne fotoanot, 
14A. 

•— , on Tolcanic rocks, 169. 187. 474. 

Sea, proofs that it has not sunk, but 
that the land has been raised, 91. 

Sea-ordiins, figures of, 48, 49. 

jSeale, Mr., on dikes in St. Helena, 183. 

Sedgwidi, ProilMsor, on garnets in alter, 
ed rocks, lt6. 

, on changes caused by truf dike, 

178. 

, on intrasion of trap, 18U 

on granite Teins, 910. 
on stratification. Joints, and cleav- 
age, 9S0. 939. 938. 

««-, on lower New Red sandstone, 413. 

>, on the Magnesian Uaettone, 96. 

417. 
.i— , en the Coal, 499. 
^•^ on Canbrian system, 456. 465. 486. 
.— ., on granite of Dartmoor, 499. 
~— ., on gruiite of Brora, 605. 
— — , on geology of Arran, 510. 
Segregation, veins formed by, 914. 
Seine, chalk needles in valley of, 385. 
Semi-opal, inftisoria fossil in, 63. 
'Serpentine, 164. 167. 296. 
SerpttLeaa fossils, inrove slow deposition 

of strata, 46. 
Sewalik hills, fossils of the, 319. 
Shale defined, 97. 

Shells, marine, rules for recognising, 61. 
, freshwater i$ee figures), 60, 61. 69, 

63,64. 
__, common to, rivers and the sea, 63. 

. amphibious 63. 

, terrestrial (see/lgurei), 63, 64. 

•— , Inferences drawn from the shi^ 

of the mouths of, 64, 66. 
ISheppey, isle of, fossils, 309. 311. 
Shetland, granitet of, 908» 
Ships, tossil, 996. 



Sidfy. teillafj stifltn ofV 94. 
Sidbw hiUs, sectkm of the, 99. ' 

, trap rocks of, 483.: 

A%aBarte, Sg«ras ef , 499. 

, erect position of in Coal strata, 

447. 
^ex, in solution, source of, 87, 88.- 
Slliceoas limestone described, 99. 
Silurian strata, origin of flame, 4t6# 

, table of auceesrioa ef, 45rv 

, Uppec,fDasfls of, 468: 

, Lower, fossils d, 460. 

> , Low, trap rocks of, 484* 

, in ITorw^ and Sweden, 94. 46t. 

463. 

, horixoDtal, ttS. 

, in N. America, 469. 

, granite altering, 600. 

Skaptar Joknl, eroptlen ct^ 473. ^ ■ 
Sky, trap dikes in, 169, 170, 17K 
-.— , ooluaniBr basalt o^ 189. 

, rocks altered by tt^ In, 179* 

Slaty deavage, 230. 938. 
Slikensides, 117. ]9fl. 
Snowdon, fbsslts of, 46ft. 
Sjjdertelje, recent strata at, 9M* 
Solenhofen fossils, 381. 
Solfatara. rocks of, deooOkpOM, 10w' 
Sorgenfri, dike at,» 174. 
Sorting power of water, 34. 
SpaurngtUt figures of, 48, 49. 
SphamiUet ag a ric( fii rmii, 340. 
^ienoptertMf figures of, 351.498* ■ 
Spirtfera, figures of, 41&. 437. 
Sponge in fiint, 319. 
SpongtUa in tripoii, SB. 
Springs, calcazeous, 71 . 896. 
Staffs, rock of, volcanic, 18« 
Stammerham, cracks in cligr aft, 3S9. 
Stations of species, 375. 
Steatite, 167. 

Steeple Ashton, fosdl coral ftom, 371. 
Sternberg on fosdl coal plants, 497. 
Stig^uurfap, figures of, 434. 
Stirling Castle, rock of altered, 178. 
Stokes, Mr., on lapidiflcatioo of fbsril 

wood, 89. 

, on structure of Orthocerata, 4G9. 

Stone-lilies, fossfl, 372. 374. 
Stonesfield slate, fossils of, 389. 
Strata, term defined, 5. 
—^t original horisontality of, 35. 79. 
— >-, thinning out of, explained, 37. 

, parallelism of, 35. 

, ripple-marked, 40. 

, gradual deposition of, indicated by 

fossils, 44. 57.374. 
, their mineral compQritioB, 95. . 



IVDSX. 



541 



Serata, GoaiDlldatlini of; 70. 

, horizontal it great heigfatt, 94. 

•— ^, sometimei reyerged, US. 873. 

— — , age of, how deteraiiiiad, S71. 467. 

487. 511. 
, foMilifarous, dutmologioal w- 

raagemeDt of, 968. S79. 
.— — , -oldest gometimes horiaontal, 464. 
— ~, conversion of fossiliferous into 

metamorphic, 613. 
Stratludrd, fissures caused by decom- 
posed trap dikes» 170. 
Stratheden, trap rocks of, 489. 
Strathmora, TsUey of, 99. 4d8. 
Stratification, forms and caiues of, 5. 38. 

38.40.44.98. 115. 

, proof of aqueous origin, 7. 

— «— of deposits in lakes and estuaries, 

6.7. 
-*— , planes of, liow for parallel, 36. 

, distinct from deayage, 230. 

Stratum defined, 5. 

Strickland, Mr., on tertiary ttrate, 899. 

Strike and dip e3q>lained, 106. 

, sometimes not altered by intruded 

granite, 218. 
Stromboli, 471. 476. 491. 
Studer, M., on alternation of gneiss and 

fossiliferous rocks in the Alps, 618. 
Stntcbbury, Mr., on fossil reptiles, 417. 
Subapennines, intentratifled tnff oi; 476. 
Subsidence of land, 95, 96. 

, in Cretaceous period, 338. 

, in Wealden period, 368. 367. 

, in Carboniferous period, 443. 

Succinea eUmgaiay 68. 

Suffolk, fi^shwater strata In, 899. 

, Crag of, described, 300. 

Soishnish, trap rodis of, 171. 
Superior, Lake, recent deposits in, 76. 
Superposition, relative age of strata 

shown by, 878. 
Sutton, section at, 308. 
Sweden, gradual rising of land in, 96. 

, Recent and Tertiary strata of, 394. 

^1 Silurian strata, horizontal in, 94. 

461. 463. 
Swiss Alps, altered rocks of, 615. 
Syenite described, 801. 
Syenitic greenstone described, 164. 164. 
Synclinal line described, 100. 110. 

T. 
Table Mountain, stratificati<m of, 94. 

, granite veins in, 808. 

Talc, 167. 

Taloose gneiss, 886. 
Taloose granite, 801. 



Taloose schist, 816. 

Tattingstone, crag strata at, 301. 

Tephrine, 166. 

Tercis, chalk of, 340. 

, chalk and irolcaiiie tuff, attvnMtkig 

at, 479. 
Ter^eUumfiu^rme, 310. ^ 
TerebratultB^ fossil, figures of, 316. 381. 

379.468. 
Tcredtna^ fossil wood bored by, 60. 
Teredo navaUSt wood bored by, 49, 80. 
Terminology, 343. 
Tertiary formations, their teiatire posi- 

ti(m, fossils, ftc, 888. 
'~—, divisible into four groi^M, 888. 

, how classified, 383. 

->->,ofdifferent countries described, 998. 
, how distinguished ftom Beoent, 

898. 

, volcanic rocks, 476. 

— — , plutonic rocks, 494. 
Testacea. See Shells. 
Thermal ocean, theory of, 264. 
Thinning out of formations, 877. 
Thirria, M., on the Oolite, 401, 
Thun, lake of, land shells drifted into, 

u9. 
Thunnann, M., on the Swiss Jura, 109. 

376. 
Tisbury, fossil coral from, 371. 
Toadstone, 165. 
Tourmaline, 167. 
Toumedos, chalk needles at, 336. 
Trachyte described, 154. 165. 
, analogy in composition of granite 

and, 804. 

and basalt, relative position of, 474. 

Transition strata and fossils, 868. 262. 

455. 
Trap conglomerates, 191. 
Trap dikes described, 168. 

, rocks altered by, 170. 176. 

, their abrupt termination caused by 

denudation, 189. 470. 
Trap rocks described, 142. 

, name whence derived, 142. 

, step-like appearance of, 148. 

, changes caused by, 170. 176. 

-, intrusion of, between strata, 181. 

-— , their relation to modem lavas, 188. 

193. 

, pass into granite, 808. 

, regarded by Werner as aqueous 

deposits, 360. 

, on the different ages of, 467. 

. See also Volcanic rodu. 

Trap tuff described, 168. 
Tra&b,166. 



B B 



548 



IKDSX. 



Travertin deposited bf springs, 71. 

Tree-ferns, figures of, 430. 

ThBM inCoalstrata, erect position of, 



Treuil coal-mine, vertical trees in, 445. 
Trigonia gibbosa^ 376. 
Tripoli composed of inftuoria» 51. 
Trodtui^ and cast of the same, 80. 
Tronstad Strand, secUon on beach at, 

3L4. 
Trough, or basin, described, 100. 
Tuflr, volcanic, 12. 158. 

, imbedding of fossils in, 472. 

Tufaceous conglomerates, 159. 
Turner, Dr., on combinations formed 

by mineral matter when in a nascent 

sUte, 86. 
->-^, on source of sUex in solution, 88. 
TurriUtes eostatus, 317. 
Tuscany, volcanic rocks of, 476. 

, calcareous springs of, 526. 

Tynedale fault, 121. 

U. 

Unconformable stratification, 115. 

Underlying rocks, term proposed for 
granites, 17. 215. 

Unto littoralis, 61. 

Upheaval of extensive n^jisses of hori- 
zontal strata, 93. 

Upper New Red sandstone and fossils, 
408. 

V. 

Val di Note, volcanic rocks of the, 190. 
Valley of Bray, 815. 362. 
Vr.lleys of denudation, 126. 
Valorslne granite, veins of the, 211. 

517. 
Valvata, 62. 
Veins, granitic, 204. 

• , metalliferous, 212. 

, of segregation. 214. 

. See Dikes. 

Velay, volcanic rocks of, 11. 

Vertical strata parts of great curves, 98. 

Vesuvius, 471. 476. 

Vlcentln, columnar basalt in the, 185. 

Virlet, M., on corrosion of rocks by 

gases, 249. 
— — , on cretaceous rocks of the Morea, 

342. 
■ , on volcanic rocks of the Morea, 

478. 481. 
Vivarais, volcanic rocks of, 11. 
Volcanic eruptions, number of in a 

century, 491 . 



Volcanic dik«s described, 168. 

, rodu altered by, 175. 

Volcanic griu, 159. 

Vtdcanic rocks described, 11. 141. 147. 
161. 

— — , produce a fertile soil, 144. 

— .— , analysis of minerals found in, 166. 

'—t their fusibility, 160. 

, their relation to trap, 188. 193. 

— — , denudation of, shown by dikes, 
189. 

— .— , submarine, 13. 188. 

, on the different ages of, 14. 467. 

, age of, how determined, 467. 

■ ■ . See also Trap rocks. 

Volcanic tuff described, 12. 158. 

, Imbedding of fossils in, 471, 472. 

Volcanos, extinct, of different coun- 
tries, 11. 13. 145. 

, cones and craters of, how formed, 

145. 

, all near the sea, 192. 

VoUxia brevifolia, 409. 

Volutes, figures of. 305. 310. 

Von Buch, OB rise of land in Sweden, 
.95. 

, on granite of Norway, 215. 501. 

— i— , on altered Oolite, 499. 

Von Decheu, M., on granite veins, 
210. 

— — , on isle of Arran, 510. 

W. 

WackS described, 165. 

Waller cited, 263. 

Water, sorting power of, 34. 

, levelling power of, 35. 37. 

Watt, G., experiments of, 246. 

Wealden strata, position and subdivi- 
sions of, 345. 

, fossils of, 346 to 351. 361, 362, 363. 

365. 

, passage of beneath chalk, 351. 

— ^, how formed, 352. 359. 

.— -, extent of, 361. 

.-.— , age of, 364. 

Webster, Mr., on dirt^bed in Port- 
land* 354. 

Welnbohla, granite of, covering chalk, 
505. 

Wenlock formation, 460. 

Werner, his classification of rocks, 
258. 

West Indies, recent and tertiary strata 
In, 296. 

Westphalia, cretaceous rocks of, 333. 

Whin-SllI, intruded trap, 181. 

Whinstone, 165. 



1)7I>EX« 



549 



Wblte Mountains, granite veins in, 490. 

Whitestone, 226. 

Wltham, Mr., on fossil coal plants, B2. 
449. 

Wood, recent and fossU, drilled by per- 
forating moUusca, 49, 50. 

-^, fossil, magnified portion of, 82. 

— , experiments to Ulastrate the pe- 
trifaction of, 84. 

, rate of its lapidiflcation, 89. 

Wrekin, trap tufik of the, 484. 



Y. 

Yarmouth saads, new channel in, aOT. 
Yorkshire, Oolite of, 384. 

Z. 

Zamia, fossil, in Portland, 353. 
— , recent, figure of, 354. 
Zechstein and fossils of, 415. 417. 
Zoophytes, limestone formed by, 71 . 
, fossil, in OoUte, 371 . 373. 



THE END. 



lA>ifi>oir: 

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